Most likely would work, it would down clock the Titan card however so not a vary cost effective SLI configuration. Would be better running single card with the Titan.
Intel 14900KF ~ Asus MZ790A ~ 48GB DDR5 ~ RTX 3090 Ti ~ Crucial T700 SSD ~ SeaSonic TX-1600 ~ Praxis WetBench ~ Full Custom Water.
In some games a 2080 Ti struggles to maintain a solid 60FPS at 4k resolution. If the game supports SLI, two of them will ensure you never dip below 60FPS. Or, if you have a 4k 144Hz monitor such as Braegnok has, then two 2080 Ti's or Titan RTX's is a real treat.
Nate is, of course, correct...you need same memory amount etc to SLI properly...you can find hacked drivers for same gen stuff but it's always a compromise and might not work well...