Do you mean you want the script’s own path so you can reference a file next to the script? Try this:
$scriptpath = $MyInvocation.MyCommand.Path
$dir = Split-Path $scriptpath
Write-host "My directory is $dir"
You can get a lot of info from $MyInvocation and its properties.
If you want to reference a file in the current working directory, you can use Resolve-Path or Get-ChildItem:
$filepath = Resolve-Path "somefile.txt"
EDIT (based on comment from OP):
# temporarily change to the correct folder
Push-Location $dir
# do stuff, call ant, etc
# now back to previous directory
Pop-Location
There’s probably other ways of achieving something similar using Invoke-Command as well.