C:\ProgramData\Maptech\Terrain Navigator Pro\Templates
Note that ProgramData (which is not the same as Program Files) is a hidden, system folder. Use the View menu in Windows File Explorer to enable the showing of Hidden Files and Folders.
Then, copy the desired .TPL files from one PC to the other, placing the .TPL files in the same C:\ProgramData\Maptech\Terrain Navigator Pro\Templates folder. Start Terrain Navigator Pro, and any templates copied will be available.
Note that these directions assume that Terrain Navigator Pro is installed on the "C:\" drive. Substitute whichever drive letter TNP is installed on, if necessary.