a dermatologist would be a good choice. their specialty is skin and many of them will do office procedures assuming this growth needs to be removed. many primary care providers will do this too but you will need to talk to your own to see if this is something he or she will see. this can be many things including a retained foreign body (like a splinter).
what type of physician do i need to see if i have a growth under the skin of my thumb? . it started out as pea size and now is elongated and gets in the way when doing everyday construction. it moves and almost seems like a calcium deposit.