I'm playing the Definitive Edition of Divinity: Original Sin II on the Switch. According to the internet, in the elf cave south of Fort Joy, there is a Forgotten Cell here containing an undead knight named Lord Withermoore. It can be found by playing hide-and-seek with Moby, but I must have selected the wrong option the first time I talked to him (I don't even remember what it was!), because talking to him now gives me no options other than ending the conversation. It is apparently still possible to find the dirt mound covering the hatch leading to the Forgotten Cell on my own, but I can't find it.
This image apparently shows the location of the dirt mound, but the only thing there in my game is a hole in the wall, which when interacted with (as Lohse, Sebille, Fane, and the Red Prince) just gives the message "This hole is too small for you to squeeze into."
This Fandom.com page implies that the dirt mound can be found with sufficient Wits. All of my characters' Wits are currently at 10. What is the minimum Wits needed to see the dirt mound? If I have enough Wits, does the dirt mound show up automatically or do I need to do something to trigger a search of the area?