This question is not to point at mistakes, my question is bowing down to my guru (Velukkudi Krishnan) to enlighten me. I’m sorry if I am wrong and please do correct me.
Parikshith attained Moksha after the preaching of Srimad Bhagvatham and people who reach Vaikuntam never returns back. In the last episodes of Mahabharata, when Janamejayan request Vedavyasa to show his father Parkishith. Vedavyasar brings him back from the pond, if Parikshith has already attained moksha how was he brought back? I am sure it is my lack of knowledge and this is just to clarify my doubts.