I don't know what model Epson scanner you are using, but the scanner itself should allow you to select a colour working space profile at the scan stage itself, for example sRGB, Adobe RGB(98), ProPhoto RGB. If you were to scan your images with one of these profiles embedded in the scan, you would not get this warning from Photoshop. Depending on what you are scanning, the recommended colour space in the scan could differ, so I won't make any firm recommendations because I don't know enough about what you are doing. That said, it is probably safe to scan your images in Adobe RGB(98). If you cannot select a colour working space for the scanner, then the Photoshop dialogue warning you of a missing profile gives you a drop down menu for selecting the colour space - all of the above choices would be there, with same tentative recommendation.