A UVB light is not necessarily a must. Some use them, some don’t. I like to make sure I’m covered so I use one.
Do you already have a tank/vivarium? Because if you choose to use a UVB lamp, the strength you need is determined by how far it is between the surface of the lamp to the top of the skink.
And how many lamps you “need” would be determined by how you heat your viv. Most (I think...?) UVB lamps put out light and emit heat. Generally the UVB lamp is placed over the basking spot (a BTS tanning salon if you will

). If you can achieve the right temperatures with your UVB lamp, then there would be no
need for any more lamps.
If you, however, need more heat-sources to achieve the right temperature gradient, you can either add a regular lamp, a ceramic heating-lamp, a heating mat under the substrate, or anything else you find appropriate that gets your temperatures on both sides of the viv to where they need to be.
Oh, and welcome!

Breeder and keeper of Meraukes from 2010 to 2022.