What is the meaning of the following phrase;
Due cognisance is taken of you reticence regarding item 2
I can not understand anything.
This appears to be a typo. The sentence should read
Due cognisance is taken of your reticence regarding item 2
In this case, your reticence regarding item 2 is the object of the preposition of.
The sentence means, roughly, "We notice your reluctance to speak about item #2." It's phrased in the passive voice, so it is better paraphrased as, "Your reluctance to speak about item #2 has been noticed."
To take cognizance of something means to acknowledge or notice it. Here, the thing being noticed is your reticence (or reluctance to speak) about item 2.