What does one means when he says you should be adept at W2 1099 c2c?

I believe the person is referring to Tax paperwork. The W-2 and W-4 is a form you fill out that sets the number of deductions you claim for that year. This determines the amount of taxes that will be taken out of your paycheck. The 10-99 is a form that when an employer pays you by the job, at the end of the year, they will give you a 10-99 form listing the amount you have been paid by them and it is your responsibility to pay the taxes on this amount. This is the form of choice for contractors and sub contractors.