Even though together these two players give the Bucks the quickest backcourt in the NBA, Jennings and Ellis are two similar players, who don't fit well together. The answer to this situation would be to trade either players, more likely Monta Ellis, but trading Ellis wouldn't be a smart decision for the Bucks.
The Milwaukee Bucks, even with their struggles, are still in the playoff race and if the Bucks would trade Ellis, they would most likely not get any talented young players but instead a bad contract or players who wouldn't be able to fill in for the lost production of Ellis. Monta Ellis has a player option for next season for $11 million and he is likely to opt out of his contract because he doesn't really like being in Milwaukee, and he thinks he can get more money on the open market because according to him he is a very similar player to Dwyane Wade.
The Milwaukee Bucks shouldn't trade Monta Ellis because the Bucks are still in the playoff race and if they were to trade him, they wouldn't receive enough talent to make them an even better team then they already are. The best answer is to just stick with Ellis the rest of the season and see how far they can get because at the end of the season he will decline his option and he won't be back. Next season the Bucks will be able to use the $11 million dollars they save from Ellis or other players they would trade for, to try to sign Jennings to an extension and/or use it to bring in free agents that will help this team to be competitive for the years to come.