Not a problem. If you're asked to review code, you do it to the best of your knowledge. If you are not able to comment on certain aspects because you don't fee

Not a problem. If you're asked to review code, you do it to the best of your knowledge. If you are not able to comment on certain aspects because you don't feel knowledgeable enough about the code base, say it. It's actually a good opportunity to learn about the code base. In any case, your team knows that you are new and won't be able to comment in depth and they probably also see this as a training exercise for you.