Probably by verbally preaching his ideas in German.
Certainly the Pope assumed that nailing something to a church door would make it known.
He didn't assume it would. He hoped it would, since he was unable to have the message hand delivered.
But, let's assume he Scotch taped the theses.
Let's not. As I pointed out to another poster, his theses - written in unintelligible academic Latin - would have been as useful as posting Japanese poetry.
The fact would remain that Luther did not consider the Theses to be a mere academic exercise; he sent a copy directly to Archbishop Mainz.
The Archbishop of Mainz. Albrecht the Archbishop actually lived in Halle, right next to Wittenberg.
Like many university disputations of the time, it was not purely academic - but also political and addressed current events. It was undoubtedly a challenge to Albrecht - and one probably deeply enjoyed by Frederick of Saxony. Just as Tetzel's response was, in part, a challenge to Frederick.
The fact would also remain that the Archbishop knew of Tetzel's sale of indulgences for the sins of the dead
The terminology is confused, but much more than being aware of Tetzel's activity, Albrecht recruited Tetzel personally.
Whether the Pope personally knew, the Vatican also profited.
Oh, I'm sure Leo X personally knew. But the money not taken by Albrecht actually did go to rebuilding the basilica, as far as we know, since the work was actually done.
Oddly enough, to most folks German, in 1517, would have been the unintelligible written language. While German was spoken, there was no uniform written German language. Luther's first translation of the Bible (the September Bible) wouldn't be published for another five years, and the complete German translation wouldn't be published until 1534.
Those publications were so popular in what were to become the Protestant areas (not so much so in Catholic neighborhoods) in large part because they were the first widly circulated work to reduce the spoken vernacular German into a written language.