There is a timecode generator in the Generator browser, but unfortunately, when placed in a sequence, it only reads the timecode of the sequence.
Workarounds (I'll copy from a post I made earlier on another forum):
OPTION A: Right click the clip. Command: OPEN IN TIMELINE.
Click on the clip, X, go to the Generator Browser, Click the Timecode Reader Generator, and click Q for CONNECT. You will have a timecode on the clip.
*read my commend below
OPTION B: Right click on the clip, choose: New Compound Clip. Make a new compound clip from the clip, give it an approperiate name, make sure it has the same starting timecode as the original (FCPX will normally do this automatically, as you'll see) and make sure it has the same settings as the original (again, FCPX will detect this automatically, so you just have to name the compound clip, all the rest will be automatic).
You can for instance make a smart folder with Compound Clips and other criteria, to keep track of your new Compound Clips. (because in this scenario you will have a compound clip for every original clip)
Now the comment... What's the difference between these 2 options? Simple (but important):
When using Option A, if you edit the clips in the timeline, and afterwards go to the original clips, click Open in Timeline again, and remove the Timecode Reader again for your final edit, it won't delete that Timecode Reader in the clips in the timeline. (I don't know why, I sent feedback to Apple).
When using Option B, if you edit them in the timeline, then open the compound clips later again, and remove the Timecode Reader filter (or make it invisible by pressing V), the change will trickle down to your edited timeline, removing the timecode filter there.
That's why I like to use option B, although this maybe is not a good option if you work with a lot of clips, and it also depends on what's the relationship of the timeline you send to your client and what you keep for yourself (if it's the same or not).
I can advise everyone to, like me, send Apple feedback about this, so they know this is important.
I sent feedback about making a kind of timecode HUD or something, and also being able to copy/paste timecode viewers in the Dashboard/Timecode Hud/ ...
Wow! What A workaround. I love the timecode overlay in FCP7. I use it everyday. I can't believe Apple still hasn't put this in yet. Especially with so much room in the panel around the timecode window.
You're right, I love the timecode overlay in FCP7 too. And I Also wish Apple did some better work with it in FCPX.
That being said, my workarounds don't always take as much Time as it sounds, performance is great even when making a quad image with on all 4 streams a timecode generator, and I do have some added benefits.