Jefferson Curls.

Every 9-10 days I do a Deadlift session. Looking to add in J Curls. Should I add them in pre deadlifting as warm up or post for add prehab mobility work?

Considering that your question is posted in the Foundations section but is unrelated to the actual Foundations course itself you might be better off asking this in one of the more general forum pages.

For what it’s worth, I found the J curls to be an excellent warm up for deadlifting, but I never approached loads that were challenging beyond just trying to loosen things up. Regarding J-curls as a means of progressive weighted mobility, I would probably tackle it as its own exercise with a dedicated separate day. I am not a deadlift expert, nor an expert on anything else, mind you, but this is what makes sense to me.