On etsy there is a magnetic piercing kit you can get (they are made for smart dolls but think they work for bjds too)
ive used modpodge glue cause it dries clear and peals off well. probably would be good to test it out if there is any blushing on the ear. not sure if it could pull it off or not
White water based glue that dries clear would work and you can loosen it with water when you want to remove them.
If you want studs, I'd glue them. I use Aleene's Tacky Glue, as it holds pretty well, but will wash off and not damage the doll if you change your mind. If you want dangly earrings or large hoops, you can drill holes. A pin vise works well, but I use the super cheap nail art piercing drills like these. It will take some pressure and a steady hand, just go slowly. I usually mark the ears first with a pencil to be sure I get them even.
Volks sells a pin vice set made for dolls. I’ve used it and it works just fine (especially on their dolls—they have thick earlobes), but lately I’ve been more into gluing on earrings or making dangles that hook over the top of the ear instead. Nail art jewels work really well for doll studs.
For the magnetic ear kits on Etsy, I actually saw the creator at a booth at BJDC Austin last month. The magnetic ones don't normally work for resin BJD, as the resin is too thick. She's got another style, wherein you pierce the ears of the resin BJD and stick one set of posts in. And then there are magnets on that set of posts where you can change out the earring front. For my preference, I'm planning on just gluing a set of earrings on when I eventually get around to it. The posts for the resin BJD were just awkward looking, at least in my opinion. And I would just want some simple studs, I'm not planning on changing them out frequently or anything.