I have lost the ability to keep a Skype conversation window on top of other windows after upgrading to Windows 10 with Skype for Business 2016. Previously if you right clicked the top of a conversation window you could select "Always on top" and the conversation would be planted above everything else. This is especially useful on those late night calls when working from a single monitor.
I finally figured out how to do this but it requires starting a second conversation.
Once you start a second conversation you get a “Pop this conversation out” button on the top.
Clicking on that will open the conversation into a separate window and grant you you the normal right click options.