Quinoa recipe asks for green olives, what type of olice is that exactlt (besides the color)?

Just use the green olives that you prefer, after all you are going to be the one eating it.

Many stores have olive bars where you can taste the olives before purchasing them. I'd suggest trying a few as not all green olives taste the same.

You can use whatever olive you like. Personally I like big, fat Castelveltranos but it really doesn't make much difference, although you might want something on the "meaty" side.