I think the irises in 'your' eyes need to be a bit larger: Usually only 2/3 of them are visible. -except of course if it's intentional that way, then I didn't say anything xD Otherwise the portrait is really cool so far though
Hi there! Love your paintings so far... I think for your studies you can try to observe more structurally? As in try to draw what it looks like 3-dimensionally or draw the shapes they're made of. Since it's digital you could have done that and cleaned up the sketches, I wouldn't know, but I the hands look a little bit funky to me!
I like your drawing of that guy lit from below, too... I really want to see some highlights on his hair, though! I mean that lighting is just so cool, it'll make the hair look mega-volumous with only a few strokes of white/light gray