Your Space ID is a unique numeric identifier for your Storyblok space, used for API access and integrations.
With admin access
Go to Settings → Space. Your Space ID appears at the top of the page.
Without admin access
Look at your browser's URL while logged into the space. It follows this pattern:
https://app.storyblok.com/#/me/spaces/SPACE_ID/dashboard
The number in the SPACE_ID position is your Space ID.