What's FQDN of a WORKGROUP pc?
Workgroup computers don't have an FQDN unless you specifically configure them to have one. They have only a NetBIOS (single label) name.
Also, don't confuse the Primary DNS suffix with the DNS suffix search list as assigned by DHCP because they're two different things.
It would be PCNAME.
That's PCNAME plus a dot.
For Windows PCs you can check with:
ipconfig /all
Giving:
Host Name . . . . . . . . . . . . : PCNAME
Primary Dns Suffix . . . . . . . : local
FQDN = Hostname + Primary DNS Suffix
So in this case: PCNAME.local