There are some turntables out there that already have a preamp built into their system. If you are using one with a digital interface, then, odds are, that there is already a preamp built into the table.
If you are using your turntable with a mixer, then you will not need an additional preamp, as mixers function as a preamp.
If your system has a preamp built into it, there are a few ways to tell. If you have an older system, there should be an input port that says PHONO. Conversely, if you have a newer system that has a USB port, it has a built-in preamp.