My Lenovo G50 laptop Ethernet port is faulty and is under warranty, what will my dealer most likely do?

They will either replace or repair the laptop

When did you purchase the laptop?
If it's extremely new (less than 15 days old), a good dealer should replace the laptop right away, with a new laptop (same model).
If it's somewhat old, like about a month old or more, your dealer will help you get in touch with Lenovo technical support, and arrange for a warranty repair (free of cost).
Depending on the warranty terms, Lenovo will either send you a tech at your home, or you'll have to drop your laptop at a Lenovo authorized service center.
Typical turn around time in case of dealer replacement is less than 3 days, in case of on-site Lenovo repair is about 1 business day, and in case of drop-in Lenovo repair is about 7 days. But they might take longer if the part which needs replacement isn't available at the warehouse.