Assuming you are in the US, based on some things you have said.
If you were self-employed, then expensing books related to your business is a no-brainer and would not cause you any problems with the IRS.
As an employee, before 2018 you could deduct "unreimbursed employee expenses" as long as they were normal and "necessary" subject to a few restrictions. I suspect the IRS would not argue with you about whether textbooks related to your job qualify.
However, this is one of the deductions that is gone (due to the Tax Cuts and Jobs Act). Going forward you will not be able to deduct unreimbursed employee expenses. The exception is K-12 teachers (up to $250), certain military and government employees, certain performing artists, and expenses related to a handicap. So that's a no on your books. Sorry.