Question: How can I obtain a WEP key from a laptop connected to WiFi? 

Answer: A WEP key is a fixed hex string that is implemented manually on an Access Point. Contact whoever owns the AP and get the string. Note: WEP keys are broadcast in each wireless packet and can be easily sniffed and decrypted. If you are implementing WEP I would urge you to reconsider and look at WPA2
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