Management -> Activity Monitor is my first guess.

Cheers,
Jason Lepack

One way:

EXEC sp_who

Be aware that users are not really logged in to a database.  Each user
who is logged in to the server is associated with a default database,
and anything they execute that does not have an explicit database
qualifier references that database.  But there is nothing that says a
user defaulting to database Foo could not querying database Bar, or
any other database on the system.

Roy Harvey
Beacon Falls, CT