Kinda sounds like 'so rubbish'
Doing Duolingo exercises.
Is this like the Spanish "que pasa", or the American "how are you doing" or "what's up"?
No, It is like "what are you doing right now|I'm doing my honework"
If you wanna say "qué pasa/what's up" you will say "co tam/co słychać"
It really is "What are you doing?", although sometimes it could be a bit like those, just a start of a conversation when you don't exactly care about what the person is doing. But better take it literally.
Is the o in 'co' unstressed, and therefore colored in the direction of 'a'?
It is direct 'o' sound. No coloring :)
Robisz can be translated to making and doing?