Hendyrk looks at the world eternally fascinated and analytical, seeing energy exchanges, forces at work, reactions and resistances and cataloguing how they play with each other. The deeply romanticised notion of explorers charting brave new worlds and discovering exciting new things in the strangest of places is exactly how sees his relationship with science.
See attached image for inspiration - its from an old character that never saw much table time, more victorian era so I cut the rest of as a distraction. Given his Brennarland (think Bruges) background I imagine him with blonde hair instead though. But that is pretty much how he would look at a crumpled parchment blowing along a cobblestone street while 'relaxing' with an afternoon coffee, sandwich and periodical/thesis he is catching up on. The face is fine but I'm not attached to it, the feel is more significant than the actual features.
Were he given to such things as following fashion - the science of which clearly has more factors than he is familiar with or even well equipped to see he could be quite dapper. Instead he tends toward simple and utilitarian. He would wear a buttoned shirt for preference to tied - less to get caught up in machinery or dangle into experiments. Also preferring a closer fit than might be common for similar reasons in both shirt and trousers. No jewelry.
A small satchel holds his regular note book and writing implement, a deck of playing cards and a small baton for self defence - his parents insisted on some sort of defence and tuition in it before he headed for foreign lands. It is the sort of thing some police forces (and/or low rent felons) might use.
Physically slight and maybe a sliver above average height - if he had a bit more muscle on him he'd make a good long distance runner. Generally well looked after and clean but with no fear of getting his hands dirty in the name of learning and discovery. Blond haired and blue eyed, analytical first, caring second but not uncaring or a machine inside. His scientific passion comes from a desire to make things better. He might not always think through what it is he is making better. Better cannons? Better beer? Better Lighting?
For pose/setting I'm not set on anything but upper torso Hendryk looking across desk at some artefacts of experimentation (maybe shell casing's, beams of wood with assorted damage, beakers with hunks of something in them etc) with pen in one hand scribbling notes while the other gesticulates in line with what is on his mind seems like a pretty solid fit.
Pop culture references for character more than appearance:
Jeff Goldblum in jurassic park (though probably not so charismatic but thats hardly a criticism, YMMV), Rachel Weisz in the Mummy, any geeky adorable lab tech from a police investigations themed tv show.
A dose of Paul Bettany wouldn't go amiss. Maybe a younger Giles/Anthony Stewart Head from the buffyverse.