What is the differecne between, lets say those sentences?
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もの is used for tangible objects. 面白いもの could refer to some interesting object.
こと is used for intangible objects such as concepts. 面白いこと could refer to some interesting concept.
の is used to say, for your example "interesting one." Sometimes, こと and の and transposable.
Of course, there is more nuance to all three, but what I said should explain your sentence:
”Please tell me the interesting one/‘part.’”