Right click your account name, and look behind the profile;u=, which is your userID.

In your case, https://bitcointalk.org/index.php?action=profile;u=1987696, 1987696 is your userID.
Please, in the future, refrain from posting such questions as they can easily be googled by yourself..


http://lmgtfy.com/?q=bitcointalk+where+is+my+userid gave me the correct answer in >5 seconds...