By checking you cervical mucus. They are different ways to check this but all depends what your comfortable doing.
One way: checking after you wipe from going to the bathroom
Way two: using your fingers to check. Meaning inserting either one or two, (index and middle finger)
If there is something that looks almost like egg whites then you are ovulating.
Way three: keeping track of your cycle and basal temperature. There are many apps on the phones now a days that are very helpful with keeping track of you cycle and your ovulation cycle!!