As VyOS can act as NTP server/relay there should also be an op-mode command to display all connected clients.
This can be done by ntpdc -c monlist
vyos@vyos:~$ ntpdc -c monlist remote address port local address count m ver rstr avgint lstint =============================================================================== xxx05.xxx.net 123 172.16.254.30 1 3 4 190 3 3 xxx03.xxx.net 123 172.16.254.30 1 3 4 190 16 16 xxx02.xxx.net 123 172.16.254.30 4 3 4 190 54 24 yyy01.xxx.net 123 172.16.254.30 11 3 4 190 72 76 xxx01.xxx.net 123 172.16.254.30 11 3 4 190 78 150
Proposal:
show ntp clients