Both the fork version and the fork digest are part of the eth2 field included in every node's ENR.
To extract it, you can use the ENR Viewer or any other ENR decoding tool. This screenshot shows the ENR for a node on the Spadina test network:

The eth2 field contains the following: 0x09fb0a1200000002ffffffffffffffff
- The first four bytes are the fork digest
09 fb 0a 12 - The next four bytes are the fork version
00 00 00 02 - The next four bytes are the "next" fork version
ff ff ff ff (upcoming forks, here: none) - The next four bytes is the "next" fork epoch
ff ff ff ff (upcoming forks, here: none)