T2Laser can load images formats (jpg, png, bmp etc) and vector formats (dxf, plt). Sketch is a proprietary format.
G-code is saved as .nc by default but you can use any extension you prefer, it is Grbl compatible G-code (a subset of NIST) or you can Save Machine G-code which is post processed to match various other formats that no longer follow the NIST standard.