Generic Skills (Anyone can get basic and advanced training in these)
Leadership, 
Atheletics, Agility, Small Arms

Combat Focused Skills (Only the combat class can get advanced training in these)
Assault Rifles, Weaponry, Armor

Combat Specific Skills (Only the combat class can get training in these)
Machine Guns, Grenade Launchers, Rocket Launchers, Explosives

Recon Focused Skills (Only the recon class can get advanced training in these)
Submachine Guns, Close Combat, Marksmanship

Recon Specific Skills (Only the recon class can get any training in these)
Sniper Rifles, Stealth

Engineering Focused Skills (Only the engineering class can get advanced training in these)
Shotguns, First Aid

Engineering Skills (Only the engineering class can get training in these)
Security, Construction, Medicine