What coin is John F. Kennedy on?

Not enough information to answer. Please post a new, separate question with more information:

- is it a commemorative medal or "round"?

- if not, is it a US half dollar?

- if it's a half dollar, what's its date?

Assuming you have a half dollar, only those minted from 1964 to 1969 have any extra value because they contain silver. 1964 halves contain about 1/3 of an ounce of silver while 1965-69 Kennedy halves have about 1/7 of an ounce.