I have a legacy app that connects to my SQL 2008 server. I'm trying to determine if the application is re-using it's connection to the SQL server or is creating new connections on a regular basis.
Using SQL Profiler I've audited for login events, but that appears to generate an event every time a SQL statement is executed even with apps that I know are maintaining their connection to SQL.
sp_who will give you a list of connections.
What you do is try setting the max pool size on the server and then open a few connections to the server and see if it times out, but then again that's if you want to see if the pool is being used.
Use perfmon to check. Here is some info on that ADO.NET Perfmon counters
Here is another link you may find interesting SQL Server Connection Pooling
Hope that helps.
Edit - Also you may want to check the driver information on the legacy app, example if the legacy app is using an OLEDB driver, they may have some notes on the connection pooling.