I did a clean install of windows 10 and visual studio 2015 and did not find makecert.exe anywhere. Does some other software need to be installed to get this program back?
I looked in all the folders under "C:\Program Files (x86)\Microsoft SDKs\Windows\\" and did not see it in any.
I also opened the "Developer Command Prompt for VS2015" and tried running "makecert" but it was not found.
Install the Windows SDK for Windows 10. If you still can't find it, try the Windows Driver kit.