"Co robisz?"

Translation: What are you doing?

[JedenPolska]

Kinda sounds like 'so rubbish'

[chce_polski]

Doing Duolingo exercises.

[DavidOrzec]

Is this like the Spanish "que pasa", or the American "how are you doing" or "what's up"?

[Mono_no_aware]

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"

[Mono_no_aware]

*homework

[Jellei]

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.

[BasCostBudde]

Is the o in 'co' unstressed, and therefore colored in the direction of 'a'?

[tegguinn]

It is direct 'o' sound. No coloring :)

[BuchitaBuchys]

Robisz can be translated to making and doing?

[Jellei]

Yes.