If your midsection is where you tend to accumulate the majority of your fat, keep in mind that there's no such thing as 'spot reducing.' Simply strengthening your core muscles won't strip away the BF in that area.

As far as getting your BF checked, most gyms offer a body comp analysis. Some do the first one free. If they do charge for it, it won't be much. Keep in mind, they're generally not all that precise (all depending on the competence of the trainer/assessor administering the tests) but it will give you a general idea of where you're sitting.

If you think you're sitting around 20% right now, I'd say you need to go into a cut first. Then once you've dropped your BF a bit, you can reevaluate what you want to improve on. But get your BF checked first to make sure.