I solved it by using this code:
public static bool IsCMYK(Image image)
{
var flags = (ImageFlags)image.Flags;
if (flags.HasFlag(ImageFlags.ColorSpaceCmyk) || flags.HasFlag(ImageFlags.ColorSpaceYcck))
{
return true;
}
const int PixelFormat32bppCMYK = (15 | (32 << 8));
return (int)image.PixelFormat == PixelFormat32bppCMYK;
}