I wound suggest not thinking of the pelvis as being on a twist in this image. Instead it might be helpful to think of the pelvis sitting in place, the same as it always does, but in this image it’s in a slighting three fourths position, and we are looking down at it. So just draw that as you normally would if there was no twist. As far as for the rib cage that is twisted from the pelvis a bit. A good thing to take note, is that the model here is not actually twisting, in the rib cage, as much as it first appears. The shoulder blade, of her right arm, is being pushed back and out, which makes it appear that there is more twist to the rib cage than there actually is. But if you look at the indications of her spine, you can see that the twist isn’t that major. You can see that the spine is really just twisting in between the pelvis and the rib cage, to connect those two different positions. Remember both the rib cage and the pelvis are in fixed positions, meaning they don’t themselves really deform much. The spine, the Thoracic part, is connected to the rib cage in a fixed way. When the Thoracic rotates, the rib cage is coming along for the ride. So if you understand where the spin is, that should help explain what the rib cage is doing. Just remember that, in this image, the rib cage is in a three fourths view, which means you are not just looking straight at the back of the spine, which means you are going to also see it’s natural curve, that you can always see from the side view. Don’t get that confused with the twist. In this image the model’s pelvis is slightly turning away from us to the right, and I feel the rib cage is slightly moving away from us to the left. So think of them as both being in static positions in separate three fourths view, and then attach the two using the Lumbar part of the spine. Maybe look at pictures of the rib cage in a three fourths back view to help you understand. I hope that helps, and that I didn’t say anything incorrect. That is just the best I could come up with from looking at the image. I am still learning too. I thought you hadn’t received any comments yet, but just saw that you have. Oh well, maybe this will still be helpful.

First look for a few of the boney landmarks so look for the iliac crest and the coccyx on the hips to get an idea of how that is turned. On the torso look for where the ribs jut out, the Scapula and shoulder muscles slide along the ribs so they can help you imagine the form of the ribs. Most importantly look for the line for the spine, that's where the ribs are coming out of so it will determine how they sit. I put these landmarks in red. You can try to visualize the forms with the egg / bucket method or use blocks to help get a better 3D visual (the egg shape can be harder to visualize in 3D). I added a loose 1 min gesture drawing I did, hope that helps.

Not an expert but i think drawing the figure as a robobean helps a lot with figuring out the twist! Here is how i did this pose in particular with the always great ms paint + mouse combination: Stan gives a better explanation than i can in the figure drawing course videos and notes: https://www.proko.com/course-lesson/how-to-draw-structure-in-the-body-robo-bean/notes https://www.proko.com/course-lesson/robo-bean-assignment-examples-twist/discussions