Question

When u ask someone how they been doing and they say “good”, can u say back “ oh, that’s good”

Answer 1

Yes, of course u can!

Step-by-step explanation:

Answer 2

Probably yes.

Step-by-step explanation:

When you say "oh, that's good", you're saying that it's good that they had a good time. Although you'd want to fix the capitalization, the sentence seems pretty fine to me.