It looks like that both .motn and .cdr files are used by Apple Final Cut Pro and as such, this software is the likely choice for this conversion. That is, if its even useful or possible to do it. Probably used for burning compilation of motion files, or something like that.
Convert Apple Motion motion data to Apple Final Cut Pro CD or DVD master image file.
We found one software available in the database for this conversion.
Apple macOS / Mac OS X software - convert motn to cdr on OS X
A professional video editing software from Apple
Convert from motn file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.