If you have in your veil.conf file daemon=1 or if you include -daemon in your startup command it will prevent the Veil CLI wallet from showing you the seed words phrase, even though it generates a new wallet for you!
To generate a fresh seed phrase wallet, be sure that your veil data directory is empty, except for the veil.conf file (optional), the backups folder, if you have used Veil on this computer before, and the testnet4 and or devnet folders if you run those other test environments.
Then from your program's directory, normally in Ubuntu or MacOS Terminal:
./veild -generateseed
If you are launching a testnet wallet, use -testnet or -devnet as appropriate.
./veild -testnet -generateseed
Related FAQ: Where is my data directory