I had an upvote of a comment but I did not see it, neither in my Inbox nor in reputation. Is it normal?
Reputation is less important, compared to not seeing this activity in my Inbox.
You ask about earning reputation for posting comments. Because comments are "second-class citizens" on SE, they do not accrue reputation and you are not notified of votes on them. The only thing they can actually do for you is earn you the Commentator Badge and Pundit Badge. By virtue of their absence, they can indirectly help others earn the Tumbleweed badge.