Oddly enough, I came across a YouTube short of a guy practicing dragging knee in a parking lot just a couple fo days ago. Though it can be done, it’s not a great idea, as parking lots tend to have debris or other stuff on the surfaces that make traction hard to predict.
Knee dragging is an outcome of sufficient lean angle and is generally not the objective, except for the person new to it. Often, once a rider touches a knee down, they go through a period of doing it everywhere possible, pressing their puck assertively into the pavement. Later, they minimize contact, dabbing a knee just until they make contact and using this as either a way to sense lean angle or occasionally as a way to help recover a slide.
Advice: Learn a secure hang-off position, where you can lock onto the bike with your lower body using no bar pressure. Practice this and become consistent with the position. As you corner incrementally faster and feel like your knee must be getting close, you can reach out a bit with the inside knee and see if it makes contact. If it does, the mystery evaporates and you have a definite idea of how far you are leaned over. If it doesn’t touch, you know there is a ways to go.
Focus on consistent body position, line, corner speed and throttle control. That’s the platform from which to safely go faster, which will require more lean angle. Sooner or later, your knee may touch down as a result.