What form do I need to use to "officially" select one or more Senior Member Specialty Tracks? I have been told that I must have one selected and on record at NHQ before I can attend an SLS.

Enrollment and progression in a specialty is entered using the specialty Track Module in eServices (access limited to command and certain staff as outlined below).  

Specialty Tracks Online: Professional development officers, personnel officers, administrative officers, vice commanders and commanders may request updates to specialty track assignments and ratings through eServices. Unit commanders must approve these requests and the member’s record will be automatically updated. If this request is not approved, an e-mail will go back to the requesting official explaining why the request was rejected. Access to this application is tied to these duty assignments. Aerospace education is the only specialty track you will not be able to update using this program. Contact your unit professional development officer. for more information on specialty tracks, see CAPR 50-17.