Within Ax20012 the UserOnline form no longer show the SPID, even when you are connected to the same AOS as the user.
So to be able to see which session that are using CPU and or IO, on the SQL-Server we need to configure a REGISTRY to be able to get this information, direct in SQL-Server, the document below shows how to see the AX UsersID when looking at CPU and IO at the load on SQL-Server for AX Dynamics
See full document on how , including the Scipts
TOP CPU how to show 2012 Dynamics AX users