"1. How can I confirm if RSU pre-tax amount is already included in my total W2 wage? (sorry I know best answer is to ask employer, but want to know if there are other options or they have to be put on W2 by IRS)."

I'd think you would know what your Box 1 amount should be if the stock hadn't vested.  Everything else being equal it should be the gross amount of your pay for the year, minus pre-tax deductions, (e.g., HSA contributions).  I'd think looking at your last 2016 pay stub would help you figure that out.  Having determined that amount the actual dollar figure in Box 1 would be the sum of what the Box 1 would have indicated in the absence of the vesting, plus the amount in Box 14.  Or, ask your employer.

"2. As I haven't sold vested RSU and tax was withdrawn, if they are included in W2 wage, I assume later when I receive any 1099 form from E*trade, I can claim the 'cost' for all RSUs are '0' because they are already taxed?"

No, and you certainly don't want to do that, otherwise you'd end up getting taxed twice on the value of the stocks sold.

The compensation figure on your W-2 is: (Gross number of shares vesting x per-share FMV at vesting date).

If, instead of selling stock you'd pulled money out of savings for the taxes and handed that amount to your employer your W-2 would look exactly the same as it does now.  Basically you'd be poorer in cash and richer in stock in the same amount.

Your per-share FMV for the stock is the same per-share figure your employer used to calculate the compensation and that's the per-share figure you'll use if the sale is reported to you.  If you enter $0 for the shares sold then you'd pay taxes on the entire amount of the proceeds from the sale.  But those same shares have also been included when it came to the determination of compensation reported in the W-2.  Ergo, you'd be double taxed on those shares.

Tom Young