(install directory)\MonGirlDreams-Alpha-v23.9e-pc\game\saves
Save files are listed as (pagenumber)-(slotnumber)-LT1.save, so if you saved in the last slot of the first page it would be 1-9-LT1.save.
If you're trying to mod the save file, I suggest instead using the ingame console. The instructions to activate it are easy and it's much safer than messing with the saves directly.
Moreover if you're upgrading versions (the only thing I know that could massively mess up all saves) you need to make sure you saved in the main square, then go into options and click "Update Save" to synch it up with the new version. If you don't, the saves range from unplayable to minorly inconvenienced.