How to find FSMO roles in a Domain
FSMO Roles are extremely important to Active Directory and understanding where they lie and how they all work (eg. some roles only exist once on a domain) should be at the top of your list of “things to know” if you aren’t already well versed on it.
Wiki - FSMO Explained
Windows Networking explain FSMO
Petri explanation of FSMO
I found this Technet Blog to be extremely useful in the most efficient ways to find where your roles lie.
On any domain controller, click Start, click Run, type Ntdsutil in the Open box, and then click OK.
Type roles, and then press ENTER.
Type connections, and then press ENTER.
Type connect to server
is the name of the server you want to use, and then press ENTER.
At the server connections: prompt, type q, and then press ENTER again.
At the FSMO maintenance: prompt, type Select operation target, and then press ENTER again.
At the select operation target: prompt, type List roles for connected server, and then press ENTER again.
Type q 3 times to exit the Ntdsutil prompt.
Petri has an article on the matter but i find his ways a little more involved than the technet above from Mark.
I find that no matter how confident I am that I have removed all FSMO from a domain controller before demoting it, I still use this to double check.