Which exercise allows me to get big hands?

The piano was mostly used for spreading my fingers, the spreading of the fingers makes my grip wider from doing chord or multi key playing.
Such as playing D G D, using the ring/index/ and thumb. eventually you'll do it using pinky ring and index. As your fingers continue to stretch. This process takes years, when you're done you'll have a huge grip area, my hands looked like skeleton fans, but you also work out the muscles, which helps them from looking too skinny.
Overall most people won't notice until you actually compare hands.
My finger spread is about half an inch wider than most men, my fingers are just slightly longer than most men, and my hands are just bigger.
When compared to my girlfriends hands however my hands are freakishly huge. I can cup her breast entirely with one hand and she has 36D.
Lots and lots of time, much longer then forearm or calfs.

you can make your fingers thicker gor sure, but not longer. Deadlifts have noticebaly made my fingers thicker in less then two years

Well, honestly I don't know user.
HGH and testosterone can both change bone growth. If he was using it that long I guess it is possible. This could have serious implications to his mental health though as the skull can grow out and in, his brain might be squeezed in certain areas. Does he ever complain of headaches or such?

i personally have a group of young school aged children pull on my fingers

My hands and fingers are long but really thin and my grip strength is shit.

Its usually my grip that gives way before anything else when doing deadlifts but I'm hoping after a while they will start to thicken up as I've not been lifting long

Easy fix, do you have anything heavy at home you can grip?
Just do a standing farmers walk, literally just stand there with object in hand. You can stretch if you want. Place it down, repeat on other side (repeat same stretches also to keep body equal).
Do this few minutes every day except workout days.
Or, just buy the little grip trainers and use them regularly. Either way.

selffisting 5x5 works wonders

Manual labour will thicken your hands and fingers over time. I'm talking decades though.

honestly i respect this one bodybuilding.com/exercises/detail/view/name/wrist-rotations-with-straight-bar

Not bigger but thicker, and it's not necessarily a good look if over done.

Exercise wise? You basically need to put a shit ton of tension on your fingers to thicken them up, ya don't have muscles there just tendons, so heavy grip work essentially. Hand thickness is wrenching, gripping again, and some forearm exercises work it secondarily.

But skip all that and just become a mechanic. Uncle's one and I swear that man has ogre mitts; seen him wrench a stripped bolt out of a rusted frame with his bare hands.

To get an idea of what 'bigger hands' exactly means here, these are two brothers, one who took over the family farm while the other took a desk job. Not a great look imo

my exact thought too