Is it possible/easy for me to find the current enrollment in CS390JK?

You can get it, up-to-the-minute, through myPurdue. Easy is something else.

Under Purdue Courses (on the right), select “View the Schedule of Classes”.

Do the obvious.

When you get to “Class Schedule Search”, enter or select Subject “Computer Science” and enter Course Number “39000”.

Select “Class Search” or just hit the Enter key.

Scroll down to your course and click on the blue line containing the title, etc. to get the enrollment.

You might note the section number (004) and the more important CRN (38237). Basically, one cannot do anything, e.g. register, with a class without a CRN.