I have vested RSU stocks from my long term compensation showing in box 11. Is this considered contributing or withdrawing from a nonqualified plan?

If the Restricted Stock Units vested, but are being deferred into a nonqualifying retirement plan, select "No, this is money I contributed to my nonqualified or Section 457 plan."

Box 11 may also be used when a distribution from the plan is made. The purpose of box 11 when a withdrawal is made, is to let the Social Security Administration know that this is income that was already accounted for in regard to FICA tax and also that it was not earned that tax year if the Taxpayer is retired and subject to the Earnings Test. 

If you are not making withdrawals from the plan, select No.