I was suspended from the class, for what reason I do not know.
He had been suspended from the class, but he didn’t know for what reason.
For what reason do you not wear the uniform?
Please correct the above.
The last two sentences are not incorrect. The first sentence is arguably not incorrect either, though it feels a bit stilted and one could debate the punctuation. It may be better to write it as “I was suspended from the class; I do not know for what reason.”
In conversational English it would be more usual to use “why” rather than “for what reason”.