The sp_who and sp_who2 both commands purpose is same.But the difference is,
sp_who supports the limited columns information about currently running process in the SQL Server.
sp_who2 supports some extra columns information about currently running process in the SQL Server then sp_who command.
sp_who command is documented and officially supported by the Microsoft.
sp_who2 command is undocumented and don’t have any support from Microsoft.
But mostly uses sp_who2 command for better information of the running process.
The following images show the clear information about sp_who and sp_who2.