For a 2 star rating you have to complete the mission on any difficulty and complete one of the other task which is either the Kill List target or all 3 optional objectives on the map (2 AA Guns, 2 Artillery Guns, 3 Vehicle destroy)
I create for this mission a full collectibles guide incl Kill List target and all obtional objectives. Under the video there is a timeline for both tasks
00:00 - 01 - King of the Tigers (Classified Document)
00:30 - 02 - Workbench (Alley)
00:57 - 03 - Stone Eagle
01:23 - 04 - Kill Target Challenge02:03 - 05 - Wallet (Hidden Item)
02:12 - 06 - Roughly Written Note (Personal Letter)
02:47 - 07 - Operations Dossier (Classified Document)
03:11 - 08 - Starting Location (Rural Junction)
03:38 - 09 - Stone Eagle
03:57 - 10 - An Unfinished Plea for Aid (Personal Letter)
04:31 - 11 - Vehicle Destroy (Optional Objectives)05:28 - 12 - Starting Location (Woodlands)
05:57 - 13 - Workbench (Village)
06:45 - 14 - Destroy Artillery Guns #107:06 - 15 - Debris-Covered Love Letter (Personal Letter)
07:21 - 16 - Destroy Artillery Guns #207:42 - 17 - Workbench (Castle Grounds)
08:11 - 18 - Destroy AA Guns #1
08:27 - 19 - Destroy AA Guns #209:02 - 20 - Stone Eagle
09:20 - 21 - Bronze Statue (Hidden Item)