Scenario 1:
As we discussed in comments, If you don't have the Path and ID of the workflow item then you need to use a Query to get the item like below.
Get-Item -Path "master:" -Query "/sitecore/system/Workflows//*[@@templatename='Workflow']" | Where-Object { $_.Name -eq "<Your Workflow Name>"}
So in the above query, we have to provide the location where Sitecore maintains all the workflows. i.e. /sitecore/system/Workflows
Using the above query, it will get all the items by filtering with the template name and item name.
Scenario 2:
Using the same approach we will get the children of the Workflow that we get from the query and then loop through its child items to identify the state like this.
$workflow = Get-Item -Path "master:" -Query "/sitecore/system/Workflows//*[@@templatename='Workflow']" | Where-Object { $_.Name -eq "<Your state name>"}
Get-ChildItem -ID $workflow.Id | Where-Object { $_.Name -eq "Deployed"}
Hope this helps.