Your monitor panel probably looks somewhat similar to the one in this link -
http://www.rvpartscenter.com/Product...DID=88&CID=296
A small white box (about 3" x 4.5"), on the wall, outside of the bathroom or maybe in the kitchen/dining area.
If the monitor is working correctly, when you push/hold the "Fresh" tab/button there should be a tiny indicator
light showing the fresh water level. If your monitor panel is a different design/model, it 'might' have a TEST
button/tab, which would test/check all of the tank levels at the same time.
As an added note: while looking online for interior photos of your trailer (which I didn't find, unfortunately), I read that
the Cabana line was apparently a sister-line to the Keystone Bobcat - same trailer, different graphics.
Hope this helps, and welcome to the forum.
Terri, the Chevy co-pilot