I myself do not give practical workshops for drawing in and under water. Inge Koetzier van Hooff, with whom I took my drawing lessons, does give practical sessions. She is experienced in snorkeling and drawing. In addition, she is a professional artist. Because of this, she can also provide good information and feedback on drawing techniques. At the moment she offers workshops in Lanzarote. But questions are free, so feel free to contact her. You can find more information here.