When you pay to go to an event, then you pay for a meal at the event, are you expected to leave a gratuity for the table waiters? If so how much based on what?

If you're the one paying the bill then whatever your normal gratuity is, is what applies. If it were a hosted event such as a wedding then so long as your not the one paying it wouldn't apply.

In a larger banquet type of benefit it is often added auto to the bill.

But yes, the person who pays normally does the tip

I always leave a gratuity,having been a bartender and a waitress.
I would ask the person who is paying if you can contribute to the tip if you feel so inclined.

Twenty to twenty five in a posh restaurant and 18 to 20% otherwise.
If you are paying your own dinner bill you do tip accordingly.