ممكن "mumkin" means possible it is a noun , for example هل من الممكن ان تساعدنى is it possible that you can help me .
يمكن "yumkin" is a verb means can do , for example هل يمكن ان تساعدنى can you you help me ,
يمكننى it is the verb يمكن + ن + ى the ى is the pronoun here only and it refer to the person who is talking