After completing a level you can play it on Score Attack mode or Replay. Here, you can select up to 5 challenges to go for as you replay the level. There are a variety of options, most having 3 tiers and are stackable. These can be somewhat difficult to get in one go but if you replay the level enough you should be able to get this no problem. You can also get a variety of options to help maximize your run though to be certain of it unlocking. The challenges will have a cooldown period after unlocking so if you don't get 3 in 1 go then wait for the easy ones to come available again.
The first level is fairly easy. Syria - The Prophet's Tomb
Deathless - Complete w/out dying
Deathless Survivor - Complete w/out dying on Survivor difficulty
Untouchable - Complete without taking damage
Marksman - Perform 3 headshots within 1:00 minute
Executioner - Kill 3 Enemies
Lucky Penny - Collect 3 coin caches
Puzzle Master I/II/III - solve puzzle I - under 0:35 / II - under 1:00 / III - 0:30
Collector - Collect all Archivist Maps, Gifts of Alms, Relics, and Documents
Speed Runner I/II/III - under 5:30 / 5:15 / 4:55
Chain Reaction I/II/III - achieve a combo of 55 / 65 / 75
Pickup Collector I/II/III - collect score pickups of 56 / 84 / 105
The easiest 3 would be Executioner, Untouchable, and Deathless.
There are only three enemies to shoot and they are at the end of the level. Two after a cut-scene and just make sure to not get shot. The third is a little bit forward climbing a rope before you have to jump the cavern to reach the other side via a well placed bar over the middle of the room. Be quick here, you have a little bit of time to get him but not much, and you can't die so be quick. If you get shot, miss the third guy, or die at any point in the level, just restart the whole thing. A speed run is less than 5 mins so this can be a short level if you get the hang of it.
The pickup collector is easy too if you do all three in one go. Simply pickup all the blue wisps, collectibles, and resources,; also shoot the Chinese lanterns, map specific items, and animals/enemies should put you far over the 105. For this, you can take your time and explore fully since time and chaining them together is not important, you just need to pick them up.