Answer by Nathan C for How to check if a computer have already joined a domain with Samba

You can use net ads dn 'queryhere' to search for a computer object.

For example, I can use the following to find the "Nagios" linux server in the "Servers" OU of my domain:

net ads dn 'CN=nagios,OU=Servers,DC=my,DC=domain,DC=com' cn -S DC_NAME -P -l

The -P switch makes it use the computer account to do a lookup (computer must be joined to a domain for this to work) and -l gives more verbose information. If it fails, using -d 10 will show you why.