I've listed these in another post but thought I'd copy them out into their own sticky.
Feel free to use this as reference. Thanks!
Android - Android/data/com.postudios.gk1/files
iOS - in iTunes in Apps section look in the Files panel for GK1 and select it to see list of files including saves
Steam PC - C:\Program Files (x86)\Steam\userdata\(steamid)\262000\remote\gk1
DRM-free PC - C:\Users\(username)\AppData\LocalLow\Phoenix Online Studios\GK1
Steam Mac - Users/(macusername)/Library/Application Support/Steam/userdata/(steamid)/262000/remote/unity.phoenix online studios.gk1
DRM-free Mac - Users/(macusername)/Library/Cache/Phoenix Online Studios/GK1
For Steam, rule of thumb to ensure Steam recognizes any new saves you copy in:
1. Exit Steam.
2. Rename and renumber file(s) if needed, always renumbering higher than the highest in-game save's number.
3. Move save file(s) to Steam save folder.
4. Restart Steam.
For DRM-free PC, remember to paste the path into Windows Explorer.
Otherwise, if you want to browse to that folder, you will have to change settings to display hidden files and folders:
1. First click on Start button then go to Control Panel.
2. Click Appearance and Personalization
3. And then click Folder Options.
4. Click the View tab.
5. Under Advanced settings, click "Show hidden files, folders, and drives", and then click OK.