Where?
Discussion
All of NIP-46 is about remote signing. So apps like Amber, Keycast, originally nsec bunker and nostr:nprofile1qqs8nsk2uy2w529fs8n4tx60u7z553e4yx5dy2nxhw4elgjgawpqlaspz4mhxue69uhhyetvv9ujumt0wd68ytnsw43q4hag5n has a CLI tool that can help as well.