It looks like either goat or cow hide. It's hard to tell by the pic because the nappa finish is wearing down...but judging by the grain it could be either.
Depending on what this is...I mean is it a collar, bracelet...knowing what this is might help determine the type of leather used.
It doesnt look like buffalo or lamb, but if that grain is embossed then really it could be any number of skins....but it looks like goat more than anything.
LOTS of research, and then certain amount of going and doing. Also I'd say it depends on what you're planning on doing. Making a saddle is a lot different than making armor, and TBH there are many different ways of making leather armor.