varbinary to varchar or nvarchar
This isn't really possible in general.

The full range from 0x00 to 0xFF is valid for varchar and from 0x0000 to 0xFFFF for nvarchar so it is impossible to distinguish between two bytes that represent 2 varchar characters or a single nvarchar character.

0x4141 could be 'AA' or N'䅁'

If DATALENGTH is odd then you know it is varchar though. 

Also if the text is primarily standard ASCII as in your example then it will contain a lot of 0x00 when stored as binary if nvarchar. 

This is probably not a character you expect to reasonably find at all in varchar strings so the presence of that could be taken as evidence that the string is nvarchar.