Sealing skirted bathtub
This looks like someone didn't want to cut tile to do the job right. I'm not sure the skirting material is even being used correctly. Yes, you could use white silicone caulk on both edges and seal up that corner but it would still look bad. If this was my tub, I'd pull all that skirting out or using a utility knife cut it out. Clean all the surfaces and scrape off any old caulk. Then get a bunch of 2"x 6" pieces of bullnose tile and make a border around the tub, fastening them to the wall with silicone caulk or some other adhesive within 1/8" of the tub. If planned  right, you could get two bullnosed corners and take the border down to the floor. Then caulk with a white silicone caulk all around the tub, all around the top of the border and in the vertical spaces between the tiles where you would normally grout.

This actually sounds like more work than it is. It takes some planning and you'd have to decide on the border color but afterwards you'd be glad you did it.