You need to connect over SSH or Telnet and run the command in the Router's CLI.
E.g, from my GNU/Linux PC to the VMG8924:
$ ssh admin@fe80::ee43:f6ff:fe46:c080%wlp3s0
admin@fe80::ee43:f6ff:fe46:c080%wlp3s0's password:
> ps | grep tr69c
23392 supervis 2136 R sh -c ps | grep tr69c
> exit
Bye bye. Have a nice day!!!
Connection to fe80::ee43:f6ff:fe46:c080%wlp3s0 closed.
This only shows the process-list search command being executed, so TR069 client isn't running. If it were running you'd see another process reported with the name 'tr69c'.
The web admin interface's Maintenance > TR-069 Client page should show the service is 'Disabled'. Also, without a valid ACS URL the service will fail to start and cannot be enabled from the web interface.