vSRX:
root@vSRX1> show system license
License usage: none
Licenses installed: none
root@vSRX1> request system license ?
Possible completions:
add Add license keys from file, local or from server
delete Delete license keys
save Save license keys to file, local or to server
update Start autoupdate license keys from LMS servers
root@vSRX1> request system license update trial
Trying to update trial license keys from https://ae1.juniper.net, use 'show system license' to check status.