Granting access to the Job Activity Monitor
In order to give some privileged users access to xp_sqlagent_enum_jobs we did the following. 


Create a Database Role in master named something like SQLAgentJobManager.
Granted that role EXECUTE rights on xp_sqlagent_enum_jobs.


Then via Logins or a Domain group, granted users a membership in the SQLAgentJobManager role in master. 

EDIT: The way we implement this permission is through Domain Group login(s) such as (SQLAgentJobManagerGroup). Then add the group login to master's SQLAgentJobManager role (for running xp_sqlagent_enum_jobs) and to msdb's SQLAgentReaderRole or SQLAgentUserRole.

After that we always add or remove logins from the SQLAgentJobManagerGroup to control the group membership for those rights.