If you're missing sharing options in your upgrade to El Capitan (10.11), here's your solution.
If sharing options and Markup are missing after you install OS X Yosemite - Apple Support
Not only does this fix sharing for the Finder contextual menu, but also in Safari and Notification Center as well! No restart required either.
This procedure solves the problem only temporarily. If I log out of my user account and then log back in, the issue returns. How can I solve it permanently??
It looks like this is how. Found it in a discussion (this forum) for a similar problem in Yosemite. Note YMMV. I'm no pro. It worked for me and I'm experiencing no other issues.
The solution to the missing share options is to produce a new UUID.
Go to System Prefs > Users & Groups (authenticate if necessary to make changes). CTRL-Click on your name in the list at left > Advanced Options. Select Create New next to UUID. Restart. Will likely have to provide password for iCloud and select the extensions you want in the Extensions System Pref pane, but that’s it!
I followed this procedure and rashly went ahead with creating a new UUID despite the warnings generated by System Prefs about possibly damaging the account. It cured the missing sharing options but I wonder if I've stored up further problems. The UUID now doesn't match that showing in the Hardware Overview section of 'About this Mac'. Should I be worried by that and, if necessary, would it be possible to restore the original UUID?
Missing Sharing Options in El Capitan
