Can same volume can contain both LUN and NAS ?
In theory yes, but it isn't recommended. A LUN on NetApp filer is a special file presented via block protocol, so potentially you can have LUN(s) & regular files for sharing over CIFS/NFS in the same volume (again - not recommended)
How Can i find the capacity (Used or free) for block and file part for netapp filer?
That's a bit more complicated, but in principle you should use dedicated volumes for LUNs, which should make checking capacity fairly straightforward (e.g. by using System Manager, or from CLI using commands like df)