Ya que te empeñas en ir allá
 

Here is another phrase from Tintin comic book.

CONTEXT: He is talking about recruiting a guide to go hiking with.

PHRASE: Ya que te empenas en ir alla.

"Empeñarse en" means to have a strong will to do something, to insist on doing something.

So it means "I already insisted that you go there" ?

Oh no. You have to look at the person. It says "te empeñas", so they're talking to "you", not "I". ;)