One of the potential villains for the second season could be Nuke (Wil Traval) after his backstory and relationships being set up in Jessica Jones season one.
Jessica does not have the most well-known comic book villain gallery, admittedly, so Jessica Jones showrunner Melissa Rosenberg should be able to have her choice as the main bad guy (or gal).
After focusing heavily on a single villain in season 1, it appears that Jessica and friends could have more enemies this time around.
Even Daredevil has used multiple villains in both season that all connect to the larger villain at play.