Answer
My logic would be to use a genetic screen to identify mutations in the Gort receptor by comparing the response of the wild type Klaatu barada niko cells to the +(+R) and -(-S) structural isomers of Gort. If the response to the +(+R) isomer is significantly different from the response to the -(-S) isomer, then this suggests that the FUD gene encodes a Gort receptor. If the response to both isomers is similar, then this suggests that the FUD gene does not encode a Gort receptor.