I... Don't actually think Wisps can eat??? Back on their home planet, they mostly just lived out in the nature... They're made of energy, and they seem to naturally replenish themselves after using some for Color powers. Though they CAN be completely drained of energy, which seems to entirely stop the regeneration and turn them into a Nega-Wisp. Let's maybe not do that.
Typically peaceful, playful, friendly and social creatures.
...No mention of food anywhere, but you could make some progress if you offer it a game? Maybe if Cobalt wants, you could take turns playing hide-and-seek. It's simple to learn, and since the Jade Wisp is already hiding, it might feel more comfortable with participating.
"I thought they eat since some Wisps have mouths, like Jade here."
"A game? Hm, that is true, Wisps do like to play... Maybe that won't be a bad idea. Hey, Cobalt, you want to play a little hide and seek?"
"It's simple. One of us hides, while the other covers their eyes, counts, then seeks. You go hide while I count to ten. You can hide anywhere you want, just make sure to stay inside, you ready?"
"Alright, here I go." Silver covers his eyes. "1... 2... 3... 4..."
Cobalt already finds a hiding spot: under the couch.
"9... 10! Here I come!" Silver uncovers his eyes and starts looking around. He already spotted Cobalt under the couch, but he pretends to not notice and started looking around. "Cobalt, where did you go? Coobaaalt."
He checks the rooms while calling out to the Chao. "Where are you hiding, you silly Chao?" Cobalt snickered from their hiding spot, meanwhile the Wisp is peeking halfway out to watch.
"Found you!" Cobalt giggled as they're found. "Alright, now it's your turn to find me. Count to ten, and no peeking."
"Chachao!" Cobalt covered their eyes. "Chao... chao... chao... chao..."
Silver just hid on the space on top of the fridge. Cobalt finished counting and starts looking for him, but it didn't take long for the Chao to find him. "Aww, you found me. Heh heh."
He climbed off the fridge and spotted the Wisp peeking out. It hides partway into its bucket upon being seen.
"Hey, do you want to play too?" Silver asked it softly. The Wisp came back out a little more, and nodded a little. "You seem like a good hider. How about you go hide while me and Cobalt seek?"
The Wisp nodded. "Alright." As soon as Silver and Cobalt covered their eyes and started counting, the Wisp didn't waste a second to go hiding. When the duo were finished counting, the jade Wisp was no longer in the pail.
Time to seek the Wisp, though a Wisp that can easily phase through things might prove to be a little trickier than initially thought.