So, I know that た and ない are attributive such as: 知らない人 - a person that I don't know of (that they existed? still figuring out 分かる vs 知る)
but can you use any form of a verb to be attributive? 知れる人 - a person I could learn of? (potential form)
This would probably never be used, but grammatically is it correct?
Is every form of Japanese verbs attributive?
No. The imperative form and the hypothetical form never modify a noun. 知れ人 and 知れば人 are always wrong.
Most other "forms" (or strictly speaking, 助動詞) work attributively, but a few have a special attributive version. In particular, forms that end with -だ/-です (知りそうだ, 知るようだ) becomes -な when used attributively (知りそうな人, 知るような人).
In classical Japanese, many verbs, adjectives and 助動詞 looked different when used attributively (e.g., 日落つ = "The sun sets", 落つる日 = "the sun that sets").
It's more than attributive usage - it's actually a relative clause, because it can be a whole sentence (clause) before a verb.
今日買った本 book that (I) bought yesterday
本を買った人man that bought a book
Etc
So it can be past, present, negative, ている form, whatever. However, masu forms are not used in relative clauses.
