Do I require a comma after oh in this sentence: Oh, god, yes, it is really nice. Or should it be: Oh god, yes, it is really nice.
Or is either of them fine?
It depends- if the person said Oh God as a single unit to express exasperation, etc, then I wouldn't put a comma, but if they said Oh to express surprise, then God after a pause to express a deeper realisation, you could use a comma (Oh [pause] God). The first is probably more likely in most cases IMO.