If you purchased a string of lights, how could you determine if the lights were wired in series or
parallel?

A series circuit is when the connections are made successively, this means that at the output terminal of a device it is connected to the input terminal of the next device

To know if the string of lights is connected in series we can disconnect a light bulb and if the rest of the light bulbs after that turn off, it means that they are connected in series

A parallel circuit is a connection of devices in which the input terminals of all connected devices coincide with each other, as do the output terminals

If we want to know if the string of lights is connected in parallel we can disconnect a bulb from the chain, and if the rest of the bulbs after that continue to function normally then they are connected in parallel