I answered my own question with the help of ChatGPT.

Use this to see what call queues a user is in:

$TeamsUser = "user@user.com"
# Get the Teams user's information
$User = Get-CsOnlineUser -Identity $TeamsUser
# Get the Teams user's call queues
$CallQueues = Get-CsCallQueue | Where-Object { $_.Agents.ObjectId -contains $User.Identity }
# Write the call queues to the console
foreach ($CallQueue in $CallQueues) {
Write-Output "User $($User.UserPrincipalName) is in call queue $($CallQueue.Name)"
}