C:\ProgramData\Maptech\Terrain Navigator Pro\Templates
Note: ProgramData (which is not the same as Program Files) is a hidden, system folder. Use the View menu/tab in Windows File Explorer to show hidden items.
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.