"You are strong, just like an elephant."
Translation:Je bent sterk, net zoals een olifant.
Both 'jij' and 'je' are interchangeable in this sentence. :)
Since the use of a marked (jij) and unmarked (je) pronoun really depends on the context, and the fact that the sentences do not really have any, you can almost always use both and if one is missing, it's likely a mistake on our part. ;)
'jij' is sometimes also used to emphasize that a specific person is being addressed:
'Je moet dat doen' puts the emphasis on the action.
'Jij moet dat doen' may emphasize that a specific person must perform the action.
They are not always interchangeable though:
'Het bedrag wordt je uitbetaald'. In this case 'je' is the 'meewerkend voorwerp' (indirect object) and it can't be replaced with 'jij'.