How do I find out who owns the rights to a song?

 The MLC's public search database has become the go to place for reliable publishing information.

https://portal.themlc.com/search#work.

Please note whenever possible, confirm writer and publisher information from a reliable music industry source such as public search databases at PRO sites (SESAC, ASCAP, BMI, etc) as well as publisher sites such as app.musicservices.com.