Need to give user ability to duplicate apps he does not own

[rittermd]

I have a Developer who is not an Admin.

I need him to be able to duplicate any app into his work area even if he is not the owner.  I do not want to make him an Admin.

What rule do I need to modify or how can I do this?

[Gysbert_Wassenaar]

I think you'll have to use a modified version of a content admin role:

Security rules example: Creating QMC content admin roles ‒ Qlik Sense‌

You can restrict further that to a specif stream or even a specific app.

[rittermd]

What is the normal/best practice for sharing apps that are created by one person and then worked on by another person?

Seems like a real pain to have to export and then import.

I made the person a QlikTeamAdmin using GSS package.  They could see the Apps in the QMC and do anything to them except duplicate which was greyed out. 

[Gysbert_Wassenaar]

My guess would be having a content admin handy that can quickly change the ownership of an app.

Alternatively you can look into a tool like Platform Manager for Qlik Sense or Version Manager for Qlik Sense.