When practicing analyzing works of art, it's best to start by defining the hierarchy of lines. In other words, look for the dominant vertical, horizontal, and diagonal line in the picture. This will help speed up the process of discovery and will allow you to decipher what design scheme and golden section grid (or root rectangle) the artist chose for their composition.
In the painting below, by Terje Adler Mork, I located the dominant horizontal, vertical, and diagonal line and speculated that the artist is using a root 2 Dynamic Symmetry rectangle. Also, notice that the angles of the subject match the angles of the root 2 rectangle. This demonstrates the notion that an artist will let the angles of their subject dictate the rectangle they choose for their final design.
Below you will find additional paintings by Anna Rose Bain and Nick Alm that demonstrate possible designs in a root 2 Dynamic Symmetry rectangle.