In Act 2, Scene 3, Jessica is saying goodbye to Launcelot the clown, who is leaving his job as her father's servant to go and work for Bassanio. She says she will miss him, because his jokes lightened the mood in their house, which is otherwise "hell."
Launcelot, somewhat surprisingly, actually cries to say goodbye to Jessica. In his trademark convoluted way, he explains, "Tears exhibit my tongue." Then he adds, "Most beautiful pagan, most sweet Jew!" Clearly he has developed some affection for Jessica during his tenure as her father's servant, and possibly even has a crush on her.
Then he adds, "If a Christian did not play the knave and get thee, I am much deceived." Launcelot is speculating that perhaps Jessica is not Shylock's biological daughter, but rather that of a "Christian" who "played the knave" (seduced Shylock's wife) and "got" (begat) Jessica. He means this as a compliment, but it is delivered in his typical ribald style. We find this "compliment" coming from other characters in other places in the play. It goes like this: "Jessica, you are such a wonderful person, you cannot possibly be a real Jew!" Of course, it is hideously anti-Semitic.
You will have to determine for yourself what your feelings for Launcelot, Jessica, and Shylock are in this scene. Likely you will feel greater affection for both Jessica and Launcelot as they show their softer side. As for Shylock, this scene is supposed to make him look horrible (makes his house hell for his daughter) and pathetic (people joke that he is a cuckold). Perhaps, though, it will make you feel a bit sorry for him, or worried or defensive on his behalf.