Why does the smell of onions linger on your hands long after you have been cutting them? Even after washing your hands. I have heard that stainless steel remove odors from hands? Is it true?
There are some specific food scent removal soaps. I keep some made by 'method' by my sink. https://methodhome.com/products/kitchen-hand-wash/
Rubbing your hands on sides of a stainless steel knifes works for me. When you're done with the cutting, rub you fingers on the flat side of the knife (being careful of the blade of course!) under running cold water as if you were cleaning the knife. Do this a few times and then wash your hands and the knife with dish soap and water. It removes all the smell from my hands everytime.
Also there are various specialist hand washes available for removing food odors as ChefHopeful mentioned in his answer.
This might not exactly be an answer to the question but I do think that prevention is an alternative solution. I just prevent the issue all together by using disposable gloves when cutting onions, garlic and other strong smelling items. I personally prefer to use nitrile gloves as I find latex gloves to leave a horrid smell of there own.
Though if you have already fouled up your hands I find rubbing them with lemon juice does help. If using a recipe using freshly squeezed lemon juice you can keep the rind and flesh and rub your hands with that after cutting the onions.