Not sure, but I believe both if using boost as you will have clone volume on separate device. If this is replicated without NW knowledge (eg. at DD level as mtree replication) then you won't needed (if this would be passive box).  I use also 2xDD as active-active thus I cover both with 2xDD usable capacity (well, 7TB I believe is already included in DD type enabler so with two you get 14TB "gratis").

Are you talking about source capacity licensing? this is quite vague...we have capacity license of 50TB for 100TB usable storage( 2xDD)..which its more towards unique size of backup data...not number of copies or destination capacity

only unique copy exist at any time..the license is capacity at "source"... if the source doesnt exceed 50TB then it doesnt care how much kept at back-end(DD)..its dedupe anyway..

that's my understanding...its vague though on how this tracked

using a Capacity based license model, the capacity required is based on the client source size.

But a Traditional License model details that Data Domain licensing as follows

     The Data Domain Capacity Entitlement Enabler enables use of the Data Domain systems within the datazone up to the purchased capacity.

Are you sure storage occupied by copies is not licensed?  I would say it is - it is capacity you use that you license.

I think you are referring to license capacity (where you have only that one and eventually one for PowerSnap if using it).  That one is different and usage is monitored by special appliance module (VM actually).  I was referring to regular (legacy if you want) licenses where you use capacity add-on.