I learned that juicy fruit are considered a davar charif. Is jam or preserves made from such types of fruit also a davar charif? Why or why not?
The only juicy fruit that is charif is a lemon, see Shulchan Aruch Yoreh Deah siman 96 siff 4 & Shach about lemonade from nonjews.
There is also in the same siman siff 2 Peiros Chamutzim, fruits preserved in vinegar, like borscht. Perhaps that is what you are reffering to?
In general a davar charif loses that status when mixed with other ingredients, such as the sugar for making a jam.