I've exported a data file using Composer->Import/Export->To File. I saw a message telling me to check the logs to see if the export has completed. There is a message in the logs saying the export is finished but I can't tell where the file ended up.
Alexander, just to be sure did you export the entity or the data? If it's Data something like export Single Data, like so with default path and repository
It'll end up in the ThingworxStorage something like this
So if you have used repository and path you should navigate to ThingworxStorage\SystemRepository\20170516211624\ and you can check for the folder name if it was an export of DataTable it'll name the folder as such.