I think that it all depends on the problem that you are trying solve. Do you wish to monitor one server and verify that the services are started, or do you have a list of servers and you wish to determine which ones have TFTP and SFTP running.
Microsoft has deprecated TFTP in current versions of Windows, and I'm surprised that anyone even used it.
Again, it all depends on what you are trying to accomplish and the software that you have installed. You can test by port, process name or service name.
I don't know what name TFTP uses for service and process. You will need to look at a machine where you have it installed.
Get-Service | Where-Object -Property Name -match "tftp"
Get-Service | Where-Object -Property Name -match "ssh"
Get-Process | Where-Object -Property Name -match "tftp"
Get-Process | Where-Object -Property Name -match "ssh"
SFTP uses port 22.
Test-NetConnection -Port 22
An internet search says that TFTP uses UDP port 69. I have no way to test this but you could try this.
Get-NetUDPEndpoint -LocalPort 69