To unlock the "Draw The Line" trophy in Life is Strange 2 - Episode 2: Rules, you need to begin any one of the drawings that are available throughout the episode. There are three possible opportunities for this and you only need one of them.
The first opportunity is at the cabin in the woods. Once Sean has started cooking their food, he can approach the sliding door for the option to Go Outside and Draw. Sean sits on the veranda outside and looks into the forest. You need to look up and hold X to observe the area. Once that's done, glance back down at your sketch book and wiggle the left joystick in a circle repeatedly until that stage of the sketching is done. This drawing has four stages to complete, but you can unlock the trophy after completing just the first stage and walking away if you choose.
The second opportunity is at Claire and Stephen's house. After Claire has given Sean two chores to do, Daniel goes into hiding. After you've found him, head downstairs into the lounge area by the aquarium. In the corner to the right of the TV on the wall is a spot where you can Relax and Draw. You need to do this before you complete the chores. This drawing has at least three stages to complete, but it was broken for me and wouldn't let me get any further than the second stage. Still, even if you can't complete it, just sketching the first stage will be enough.
The third opportunity is at the Christmas market. As you arrive at the market, walk forwards towards the fake snowman and then take a left. You'll reach some picnic tables. Sit at the one table to sketch the market -- this must be done before the singer leaves the area. There are four stages to this drawing before Chris approaches and asks you to add a fifth. Like before, you can just sketch the first stage to get the trophy.