Whatcha?

-Whatcha doing Hugo?
-Nothing.
-How can you do nothing?
-Easy - just stop doing something.

It is a conversation between 2 kids.
What 'whatdra' mean? It is not used often, I think.
IS it an American word?

It means "What are you doing?" Whatcha/Wotcha is an approximate phonetic spelling of the way "What are you" is informally pronounced.
In England, "Wotcha, mate" would be an informal greeting.