Where is the Sword?
Last time the Sword was seen was in Season 4 Episode 3 titled "Breaker of Chains" as you observed yourself.
In it the sword was laid with Joffrey's corpse on his funeral.
There is no mention of sword's whereabouts afterwards however it is implied that the sword must have passed to Tommen as heir of Joffrey since there is no event which indicates that the sword was misplaced or lost.
As Tommen is dead as well, We can't say who has the sword now. Perhaps
Cersei does, As Tommen's successor.
AWOIAF wiki (Semi Canon) is correct when it says:
Upon Joffrey's death, it passes to his younger brother, Tommen
But they have cited the wrong page. They should have instead linked to the Citadel post that I have linked below. It appears to be a human error, I also initially fell for their reference but reading the chapter, it turned out the chapter was before Joffrey's demise.
To answer your question, no there is no mention in books either. It is understandable as Tommen is a child and giving him a razor sharp blade will be folly.
George R.R. Martin has confirmed that Tommen inherited the sword. See this citadel post for reference.
Widow's Wail - Newly forged out of the melted-down Ice of House Stark,
Widow's Wail was intended for King Joffrey Baratheon. Following his
death, it now belongs to his brother, King Tommen. It is a longsword.
Can a sword be buried with the bearer?
It can be. In Dunk and Egg: The Hedge Knight, Ser Duncan the Tall briefly contemplates against burying sword of his Master Ser Arlan of Pennytree with him, which implies that normal swords can be buried with their bearers.
“I’d leave your sword, but it would rust in the ground,” he said at
last, apologetic. “The gods will give you a new one, I guess. I wish
you didn’t die, ser.”
However special swords which are made of Valyrian steel aren't buried with their bearers. It is evident, by the fact, Valyrian Steel swords are inherited from Father to Son spanning over centuries e.g. Heartsbane, Long Claw, Blackfyre etc.
So it is unlikely that Widow's Wail was buried with Joffrey since none of the other Valyrian steel swords were buried with their bearers.