Are you talking about saying something publicly or saying something to the person himself?
If you meant publicly, you certainly are not allowed to say anything negative about him. For that matter, no one else is either.
If it’s privately, there are ways that one is halachically allowed to give tochacha to a parent.
I saw an interview/s with Ivanka in which she seemed to handle this issue very well. The interviewer was asking her very difficult and inappropriate (imho) questions about her father’s behavior. She refused to say anything negative about her father (in one interview, she kept saying firmly but politely, “you will have to ask him”), but she did mention that in private she is very open about stating her opinions to her father.