I didn't know you liked her' or 'I didn't know you like her'
the answer is i didnt know you like her. it acturally depends because the person might of acturally liked that person before. if the sentence before that one is about the person revealing that he likes that person then it would be i didnt know you like her. if that person doesnt like that person but did before, then it would be i didnt know you liked her. depends really. your choice.