Where is the location of pdflatex when installed through Lyx on Windows?
Modern Versions of Windows - since Windows 7 - have the
where command installed. It checks whether an executable is in one of the folders that is listed in your $PATH.
Enter the command on the cmd or in Powershell:
PS C:\Users\me> where.exe pdflatex C:\texlive\2016\bin\win32\pdflatex.exe
If Lyx installs pdflatex on the $PATH, you should be able to find it with this method.