"Whenever he see me"? Is that right?

[struck]

This defines an adverbial clause, and "Whenever" expresses a habitual action. I don't think we can say "sees", but maybe we can say "watches".

Can you explain why or why not the clause "Whenever he see me" is right or wrong?

 

[David L.]

Whenever he sees me, he always says hello.
(this might be said about some very important person, who takes the time to acknowledge me as a person by saying hello, rather than just treating me as 'unimportant')
Wheneveer he sees me, he crosses the street (to avoid me).

'sees' here has the meaning, to meet someone by chance