In addition to the existing answers: Some laptop have built-in SIM card slots. My previous laptop had one which could only be accessed by removing the battery. You could connect the built-in wifi card to the wifi provided by the router and use the mobile internet for your cheating. This has the advantages that there is no additional wifi network which the professor could easily track down and no dongle which the professor can find suspicious. On the downside, you need to have a laptop with that feature (or use a dongle which provides this feature, destroying one of the advantages).

In addition to the existing answers: some laptops have built-in SIM card slots. My previous laptop had one which could only be accessed by removing the battery. You could connect the built-in wifi card to the wifi provided by the router, and use the mobile internet for your cheating. This has the advantages that there is no additional wifi network - which the professor could easily track down - and no dongle that the professor might find suspicious. On the downside, you need to have a laptop with that feature (or use a dongle which provides this feature, destroying one of the advantages).