How will do the two witnesses know their power?

[Daniel]

Like any prophet before them they will be prompted by God to engage in certain endeavors. As to the mechanics of how they come to do what they do, you only have to look at the prophets before them and see it is a mystery how God works in prophets like this.

We do know that they are protected until the end of their ministry when they are killed. It says the whole world shall view their bodies. Not until modern times has that been possible, via satelite, people will see them on TV, the internet, or their smart phones.

Who knows, since we live in a modern age maybe they will social network on Twitter or Facebook.

In Acts we read how this lady with a spirit of divination followed Paul and his company around a few days proclaiming who they were before we read that the Holy Spirit prompted God to cast the demon out of her. He never attempted to do it until the Holy Spirit prompted him to.