wireless charging happen through a protective skin cover on the iphone?

It depends upon several factors. How to wirelessly charge your iPhone - Apple Support states:

• "Wireless charging uses magnetic induction to charge your iPhone. Don't place anything between your iPhone and the charger. Magnetic mounts, magnetic cases, or other objects between your iPhone and the charger might reduce performance or damage magnetic strips or RFID chips like those found in some credit cards, security badges, passports, and key fobs. If your case holds any of these sensitive items, remove them before charging or make sure that they aren’t between the back of your iPhone and the charger.
• If your iPhone isn't charging or is charging slowly and your iPhone has a thick case, metal case, or battery case, try removing the case."