Powershell/github issue with adding SSH key to clipboard
cat ~/.ssh/id_rsa.pub | clip should work.
More generally, if you wish to run something with the old Command Prompt syntax, you can always wrap it up in cmd /c like this: cmd /c "clip < ~/.ssh/ida_rsa.pub".
If you have the PowerShell Community Extensions(PSCX) module, you can also use:
Get-Content ~/.ssh/id_rsa.pub | Write-Clipboard
Just open the file in .ssh/id_rsa.pub with a text editor and copy it with ctrl + c.
The .ssh folder will probably be in C:\Users\YourUser\.ssh.