A:Answer Yes, research Nvidia SLI, which is specifically for using multiple video cards together. Note that your motherboard will need to support SLI and your power supply will need to be large enough to support the power draw from 2 cards. Depending on your other equipment, you could need in the neighborhood of 1000W power supply. Also note that not all games support SLI, and performance can be worse than using a single video card.
One other thing to keep in mind is that if you were previously running games at 1080p resolution, you might want to step up to a higher resolution (1440p or 4k) to make sure that the video card is fully loaded. I know it is counter-intuitive but with a 1080ti you will generally get better performance with a higher resolution (up to a point) because the lower resolutions (like 1080p) do not fully load the card and you become limited by the CPU, causing lower framerates. So before you go buy a second card try higher resolutions to make sure the GPU is fully utilized.
