I'll put together @poop's and @kuwaly's answers.
The two possibilities are are "K" for "King" or for Adolf "K" Weismann. However, the second for Weismann is incorrect. Wiki: http://k-project.wikia.com/wiki/Yashiro_Isana
After a bit of research as well as a search through the K-Project wiki, I found that Adolf's middle name isn't actually revealed in either the anime or any sources. Due to his middle name not being known, we can see that it is of little importance to the anime.
Now let's jump to the title of the last episode title, "King." We can piece the title of the anime together with the title of the final episode as the anime was leading up to the final episode, uniquely named, "King." "King," is the most likely of the two options since the plot line, use of the word "King" and the name of the final episode all relate to the one word, "King."
So the title of the anime would be, "King-Project," or "King."