Step 1: Click on your profile
Step 2: Find Modify Profile
Step 3: Click any of the below in the modified profile
Step 4: Your Profile info will appear in Top
Step 5: Find the link like this:
https://bitcointalk.org/index.php?action=profile;u=1116605;sa=account
https://bitcointalk.org/index.php?action=profile;u=1116605;sa=forumProfile
https://bitcointalk.org/index.php?action=profile;u=1116605;sa=theme
or etc.
Step 6: Find the number in link like Example in my User ID in my link is 1116605