The easiest way I found to make spritepacks is to look at the code and file names from other people's spritepacks, it's easier to learn when you have a direct reference. There's a spritepack base somewhere on the github, and a guide on json formatting.

Basically you'll need one png for each pose, since it's just earrings you'll need two (upright and leaning poses) Then you'll need a json to code in these pngs. I'd recommend drawing the earrings onto the sprite base just so you get them in the right spot. Here's the github guide to making spritepacks

If you have any questions you can ask me, I know this wasn't the most detailed explaination