You can chain “Jar Robber” to your own or your opponent’s “Pot of Greed”.
The only way to activate “Jar Robber” is to chain it to the activation of “Pot of Greed”.
“Jar Robber” must be the very next step in the chain, so if you activate “Pot of Greed” and your opponent chains “Imperial Order”, you cannot activate “Jar Robber”.