What is all the forms for unknown on Pokemon?

There isn't a single "unknown" form in Pokémon. You might be thinking of Unown, a Psychic-type Pokémon that has 26 different forms, each corresponding to a letter of the English alphabet.

Unown's Forms:

* A

* B

* C

* D

* E

* F

* G

* H

* I

* J

* K

* L

* M

* N

* O

* P

* Q

* R

* S

* T

* U

* V

* W

* X

* Y

* Z

Let me know if you had something else in mind!