The second one is charging hourly. We tend to prefer hourly fees on projects that are particularly open ended or very small scope. Our hourly rates are currently between $60 and $120 per hour depending on who is doing the work.
The word sonder exists, though. It means to probe, and in a more specific use, to test the depth of something. The word sound (as in the water feature) is a cognate, both related to the Old English sund meaning to swim, or the sea. I can't really think of an English equivalent that's specific beyond mere awareness.
Now, the Nazis and the awful, evil things they did have been covered extensively on Listverse. 9Sonderkommanden. Simply put, a Sonderkommando was someone tasked with disposing of the dead. Their more gruesome duties included ripping out the gold teeth of the dead and sweeping away the ashes of the corpses.