I'm not a UX guy myself, but our team has a rule to use some form of indicator like the "i in a circle" or ? in a circle. These are always clickable, so if you see an "i" you can click it to get the pop-up. We do avoid hovers, though our reasoning is that we're making information dense applications. Having a bunch of hover tips pop up as you're trying to navigate a table can get frustrating. If hover is used, it'll most likely be a different indicator and in the header or footer area.