Q. How do I find out if a journal is peer-reviewed or not?
The most straightforward way to do this is to check Ulrich's Periodical Directory. Once you're in it, look up the title for the journal you want to check. Once you're in the record for that particular title, click on "Additional Title Details." If the title is peer-reviewed, that section will include the term, "Refereed/Peer-reviewed."
Another angle would be to look for peer-reviewed articles in Summon and narrow your results by choosing "Limit to articles from peer-reviewed publications" under "Refine your search" (both Music Index and RILM have similar limits as well). Unfortunately, because each database codes things as peer-reviewed or not in different ways, this strategy is not fool-proof, but it's a good way of getting you onto the right track.