As far as I understand, Jews are not allowed to have a wake for a Jewish person. But, let's say for some reason, they do it, anyway. Is a Jew allowed to attend this event if s/he doesn't view the deceased? In other words, is there a problem with going to the funeral home where the wake is and standing by the coffin and just offering condolences to the deceased's family, etc. but just not viewing the dead body? Any problem of marit ayin, conveying a message of consent / approval (similar to someone attending an intermarriage), or anything else, perhaps?
dinonline was asked that question and answers
Question: Can [a Jew] attend a wake where the body is laid out in an open casket?
Answer: Certainly. In Jewish burials, the body is buried without the casket, although it is usually coverered over in respect for the deceased. There is no prohibition, however, in attending a funeral where the body is not covered over.
Sources: See Shulchan Aruch, Yoreh De’ah 362.
I am not 100% sure they understood the question, possibly because their rabbanim are based in Israel where wakes don't exist. But it clarifies the issue is not with the opened casket. Although I heard from two rabbanim one shouldn't uncover a body or watch it because it is in a state where it cannot defend itself from mazikin (would be interested if anyone has a source).
However, as the SA quoted above mentions, there is a halacha to bury the dead and our practice is to do so as quickly as practical. As such practices that unnecessarily delay the burial are frowned upon.
I thought that maybe a wake has idolatrous connotations (e.g., a source in worshipping the dead) and should be forbidden because of hukot hagoyim. But interestingly, it is possible the wake has its origins in the Jewish practice to guard the dead (shemira) before burial.
The closest I found to forbidding a wake is SA YD 343:1 which places a ban on someone who sees an unburied Jewish corpse and does not attend to its burial needs.
So ultimately this might depend on circumstances. Maybe in some cases going to a wake and participating in a voluntary delay on the funeral will be forbidden. If the funeral is delayed to wait for a close parent, maybe going there and saying tehilim is part of guarding the deceased.
As always, ask your rav before trying anything you read here in the real world.