when the question is about dp then there is not any exact method to identify the subproblems its all depend upon your practice there are various dp standard problem and in order to solve question you have to map that problem according to dp standard problem, means for solving question logic will be same but there will be some difference according to question. finally you have to identify which dp standard problem is related to your question.
eg in june15 the problem MCHEF includes knapsack dp problem.
there are various problem :- knapsack problem ,subset sum problem,rod cutting problem,longest common subsequence etc.
but if you wanna solve question apart from these then you have to do everything cracking logic ,identifying subproblems and implementing i hope it would not hurt you because it is the truth about dp. practice practice practice