Sharing Another Calendar - Outlook 2016

No, you can't share someone else's calendar that they shared with you.

Can i adjust any permissions in Exchange ?

you can give the user full manage permissions to the mailbox and that will allow them the view the calendar.

tim, that would be great - how would i do that?

In the Exchange management shell run the following:

Add-MailboxPermission -Identity "share mailbox" -User "username who needs access" -AccessRights FullAccess -InheritanceType All -AutoMapping $false

Allow about 30 minutes for AD replication and then you can add the calendar for the user.

Tim - any way to do it through admin center - not comfortable with shell yet :(

Yes, see the below link it will give you instructions, the only thing with the GUI is with the permissions the user will see the entire mailbox and not just the calendar. If you are ok with that then follow the link. The mailbox will appear in the users outlook in about 30 minutes once you assign the permissions:

https://technet.microsoft.com/en-us/library/jj919240(v=exchg.160).aspx

Fox - so i can run this:
Add-MailboxFolderPermission 'emailaddressofthecalendartobeshared:\calendar' -User 'emailaddressoftheviewer' -AccessRights Editor

Then the user can open the calendar in Outlook and edit?

Yes

OK, just ran it , ill wait a little bit and hhave the user choose open shared Calendar from Outlook 2016

Once you set the permission, open the reviewers calendar section in outlook...then right click My Calendars or Shared  Calendars or Other Calendars(choice is thiers)>Add Calendar>From Address List....pick the user's calendar to be seen

FOX solution works great, award full points to THEM.