'The person whom I ask for help is clever'

The person you're asking is the direct object of ask, and the help is an indirect one, so whom is the correct (objective) case.

However, I would - even though whom is perfectly correct - counsel leaving it out altogether and just writing one of:

• The person I ask for help is clever
• The person I am asking for help is clever
• I ask a clever person for help
• I am asking a clever person for help
• I have a clever friend I go to for help …

depending on which you mean.