I take B12 transdermally - methyl & adenosyl - with great success. had to lower my dosage because TD (80%?) had such better uptake then sublingual (5%).
The scientist who makes the above also makes a transdermal multi-B. (Company is called B12oils - in Australia.)
I've seen Science finding that magnesium works transdermally (via Epsom Salts ).
I'm certain nickel does, as a friend got a nickel necklace & his hair-nickel went through the roof.
Beyond that I don't know, but I hope it is the next frontier, because pill-popping is a pain, & there are so many issues with uptake, & gut reactions.