Ask HN: How to conduct code review of a project abandoded by original devs?

I've been asked by a friend to take a look at the project, which has been abandoned by the original devs.

Apparently, they don't want to touch it again. I don't have many details about their departure.

How would you go conduct such code/project review/analysis?

I started my own projects, joined existing projects, but never joined a project where people with knowledge about the whole architecture were gone...

P.S. Searching the web didn't help me much, the big G didn't give me any relevant blog posts, articles, etc...