Common areas to rip include the knees, just above the knees, or near the back pockets. Don’t worry about staining the jeggings, as you’ll be ripping up the fabric around the line anyway. The line shouldn’t be noticeable once you’re done ripping your jeggings.
How much distressing you do is up to you. Some people prefer lightly frayed tears, while other people want the jeans so torn only thin strands of thread remain.