Together with Samantabhadra {Fugen}, Monju is said to have attended the Historical Buddha Shakyamuni. They are often paired opposite each other on mandalas or in statuary configurations, flanking Shakyamuni. On most of Nichiren's very formal Ten Worlds Great Mandala Gohonzons; Monju and Fugen are on opposite sides of the central Daimoku, they occupy the inner most positions in the second row from the top. Namu Monju Shiri Bosatsu [南無文殊師利菩薩] is positioned directly below Namu Taho Nyorai [南無多宝如来] on the left of the mandala, which is your right.
That will work for copies the Shutei Honzon, the Denpo Honzon, and the Kito Honzon; as well as the Nittatsu & Nikken Transciptions issued by Taisekiji. Note that the Trace Gate Bodhisattvas are omitted in the SGI Nichikan Gohonzon; you will not find them there. The Mannen Kugo Daihonzon of 1274 is configured quite a bit differently, but you will find Monju in about the same position, except that Fugen is on the same {left, right facing} side, to Monju's left {your right}. On the Ichinen Sanzen Honzon; iirc, Nan {南} Mu {無} Monju {文殊} Fugen {普賢} Bosastsu {菩薩} is the third entry on your left, facing, reading right to left.
The Manjushri mantra is said to enhance explaining, debating, writing, critical thinking, memory, and so on. According to Wildmind: "Manjushri is associated with ordinary intelligence and mental accuity as well as transcendent Wisdom, and his mantra Om A Ra Pa Ca Na Dhih is said to confer intelligence. Shantideva, the author of the great Bodhicaryavatara ("Guide to the Bodhisattva’s Way of Life") is said to have gained his wisdom by communing with Manjushri by night, while appearing by day as a slovenly and lazy scholar-monk."
I added some pictures below:
Here are a couple Videos of the Manjusri Mantra with Visualizations:
Manjushri Mantra Om Ah Ra Pa Ca Na Dhih:
Manjussri Mantra / Voice of Imee Ooi:
See also: The Concept of Channeling Monjushiri Bosatsu and The Power of Threes: Three Words for Wisdom
Note that there are three primary Buddhist terms translated as Wisdom. Of these, Monju is most commonly associated with Panna / Prajna 慧 {hui / e} or 般若 {hannya}. The others are Viija / Vidya 明 {ming, myo}; which refers to objective wisdom / knowledge, science, or the object of study; and Jnana / Gnosis 智; which means subjective wisdom / knowledge, or understanding. Pra means leading to and is similar to the prefix pro, while jna means to know or comprehend, like the Greek gno / gni / gna in words like gnosis, cognition, prognosis, diagnosis, cognate, and so on.
So prajna means the the skill of discernment' that which leads knowing. I take this, on one level, as 'critical thinking;' the acquired ability to reason and think clearly; to discriminate or distinguish one object from another, to generalize or see commonalities, to employ deductive or inductive logic, to avoid the traps of logical fallacies, to remain objective or impartial, to accurately comprehend what one is reading, and so on. On a deeper level, prajna can also mean intuition or insight; the ability to perceive Emptiness (sunatta / shunyata 空 {kong, ku}) and Immediacy or Timelessness {akaliko / akalika 無時 {wushih, muji}}.
In Mahayana Buddhism, the Mahasattva Bodhisattvas are sort of like Patron Saints in Chistianity; each has their specialty. In East Asian Buddhism, Manjushri, representing prajna, is one of four primary Mahasattva Bodhisattvas. The other three are Samantabhadra 普賢 {puxian, fugen}; who represents Ethics or Morality {Sila} and Merits {punya}; Kshitigharba 地藏 {Jizo}; who represents Vows and Forbearing Patience {Kshanti}, and Avalalokiteshvara 観世音 {kuanshiyin, kanzeon}; who represents heart felt compassion. In the Nichiren context, Monju and Samantabhadra Fugen are among four Trace Gate 迹門 {shakumon} Bodhisattvas from the Lotus Sutra. The others are Bhaishajyaraja 薬王 {yakuo}; who represents healing, and Maitreya 弥勒 {miroku}; the Coming Samyaksambuddha who represents kindness {Metta / Maitri}.
I take the Trace Gate Bodhisattvas as personifications of merits (Punya {功德 {kungte, kudoku} or 功祚 {kuso}) and skills {attha/artha} that must be cultivated, earned, and acquired. Each of the four can be connected one of the first four skandhas, one the four inverted views (vipallasa / viparyasa 顚倒}, and one of the four frameworks of mindfulness. In terms of the Five Skandas, Monju relates to the third, or samjna skandha 想蘊 {so un}. Samjna is variously translated as conception, ideation, cognate, cognition, recognition, or perceptions. Sam means something like bring together or integrate, roughly the same as the prefixes co/com/con. Jna is the same as in prajna and jnana, so cognate or cognition would be literal.
Distortions of recognition lead to the third vipallasa or derangement / inverted view 蓮倒 {tendo} of perceiving nicca / niyta 常住 {joju} 常 {jo}(constancy, continuity, eternity); in that which is anicca / anitya 無常 {mujo} {inconstant, temporal}. This is corrected by practicing the third framework of mindfulness; cittanupassana or cittasati satipatthana / citta-smrtiupasthana 心念住 {shin nenju} or 心念處 {shin nencho}: mindfulness and contemplation of mental qualities and spirituality.
In this connection, "channeling" Manjushri can be seen as means of practicing mindfulness of citta 心 {shin} to correct distortions of cognition. Just as there are three nuances of wisdom; there are three meanings of ignorance. There is Avidya 無明 {mumyo (not light)} or 冥 {myo (dark)}; which is ignorance is the sense of nescience, misinformation, or an absence of information. Then there is ajnana or moha 迷 {myo (perplexion)} or 過 {ka (going over one's head)}; which is mental confusion, bewilderment, or lack of comprehension, and mudhi 癡 {chi (foolishness)} or 愚癡 {guchi (stupid)}; which is stupidity or lack of discerning skills. Cultivating prajna leads to jnana; which helps one discern vidya from misinformation. The Manjusri 'channeling' practice consists of meditative postures / gestures {ashana & mudra}, the Manjushiri mantra, and a meditative visualization. Due to length, I shall discuss methods in another entry.
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In the Buddha's Words: An Anthology of Discourses from the Pali Canon (Teachings of the Buddha)
The Lotus Sutra: A Contemporary Translation of a Buddhist Classic