Sorry for being rude but you don't need help, you need to study harder. Nobody is going to do your homework for you or at least nobody should do it That is the wrong way to become an engineer.
It was said "Need help in your electronics related homeworks? Need a seminar topic? All questions can be asked here" That's why I opened this topic. The admins can erase the question if they feel it is inappropriate to ask for any help about this question.
There can be different opinions about the purpose of getting help with homework. I think it's O.K. to ask for a way.
In the said case, the answer is traced out by giving the coding example for digits 0 to 2. You can continue the digit table for 3 to 9 and A to F.
There's a misleading point in the question "Derive the truth table of the encoder (this will be a 16x11 table)". The solution to display an arbitrary four-digit hexadecimal number isn't a decoder or a simple table. It's a digit decoder with a multiplexer, that drives the digits sequentially, needing a multiplex clock.
But I see, that the problem is given in a development kit's manual rather than a text book. Apparently the text quality needs improvement.