The local pin root is stored at /local/pins https://github.com/ipfs/go-ipfs-pinner/blob/9e800d1363c2cb23b8f82b3b1f0685b83367103a/pin.go#L22
I also made a really simple datastore debugging tool https://github.com/aschmahmann/ipfs-ds. Running ./ipfs-ds get --base=base58btc /local/pins will spit out the local pin encoded as a base58btc multibase (i.e. in this case it’ll be a CIDv0 with a z tacked onto the front of it)