I will be over the max i can earn in 2018 ( prior to 66th birthday in march 2019). are they going to take it all out at once? if so that means i won't get any social security payment for two months. And do they use the "Gross" or the amount i actually get deposited?
The countable amount of earnings for purposes of Social Security's earnings test would be any combination of gross wages and net self-employment earnings (https://www.ssa.gov/planners/retire/whileworking.html). If you know that you will earn over the exempt amount of $17,040 this year, you are supposed to notify Social Security so that they can withhold $1 of your benefits for each $2 of that you expect to earn in excess of $17,040. And, yes, they would suspend your whole benefit check for as long as it takes to withhold the necessary amount.
If you don't notify Social Security and end up earning more than $17,040 this year, you will be overpaid. Once Social Security becomes aware of the overpayment they will propose to recover it by withholding your entire check for as long as it takes to recover the overpayment. You could, however, ask them for a lower rate of withholding.
I would encourage anyone in your situation to notify Social Security as soon as you know that your earnings will require withholding of some of your benefits. I believe it's better to have any suspension of your benefits occur while you have earnings coming in to live on as opposed to having your benefits withheld at a later time when you may be more dependent on your Social Security income.