book on Nostr: what's his npub?

{ "id": "1adf2851a188f15a1366552c5e720d220ba5943afac31926b44e21f8399954ec", "pubkey": "23d1d973554196e571622b78d2cb859fd1eb579e20299358c3c38f4d903f137f", "created_at": 1778086077, "kind": 1, "tags": [ [ "e", "e01f28116c177f7c1b9fc8ad6ff706301318d291dcee21852a0a3604336d8409", "", "root" ], [ "e", "cdf30f13af0929a65caafe67c47ed81fd9faa30fff9fe660c33da1a8c8e06e41", "", "reply" ], [ "p", "ef53426a3b40ecd4181694bc409002c14f37ea1be50808829ea0dc447e988851" ], [ "p", "cdecc31c6d9406e9a7d6b0067412aa661d9d31c8035c3fd65c06301d1cac3b92" ], [ "r", "wss://relay.primal.net/" ], [ "client", "Primal Web" ] ], "content": "what's his npub?", "sig": "da7307c6b8a4e636633cc3aec62b44e52e9f80a6912b8b9b1b08ec5a368215c4f7c940cdb6320e0fee746e7bb23b7b9a091259be488bd965fc2ec6a10b965485" }