i want sell a permission on shop with VIP/donate system. 
can anyone give me an example? 

can i do it or no?

here's an example. I use the shop to sell players larger bank space which is set with perms, one of the listings looks like this:
"5 Slots": {
"buy": "20000",
"cmd": ["oxide.grant user $player.id bank.5", "oxide.revoke user $player.id bank.7", "oxide.revoke user $player.id bank.9", "oxide.revoke user $player.id bank.15", "oxide.revoke user $player.id bank.18", "oxide.revoke user $player.id bank.24", "oxide.reload Bank"],
"sell": "0"
},

Yours might be a bit more basic, and would look something like this:
"ITEMNAME": {
"buy": "PRICE",
"cmd": ["oxide.grant user $player.id PERMISSION"],
"sell": "PRICE"
},

oh yeah. thanks a lot. got it :D