How can one differentiate between humans and Jinn if Jinn manifest in the form of a human, just as Satan manifested to the Quraysh in the form of Suraqah ibn Malik?

It is not possible to definitively distinguish jinn from humans if a jinn takes on a human form, as devils can take the form of people and animals.

The most important thing a Muslim should focus on is protecting themselves from Satan by frequently engaging in remembrance (dhikr), performing supererogatory prayers (nawafil), and reciting the Quran. The Prophet, peace and blessings be upon him, said: "Do not make your houses graves; indeed, Satan flees from a house in which Surat Al-Baqarah is recited."

Whoever recites Ayat al-Kursy before sleeping, no devil will come near him until morning.

Furthermore, the last two verses of Surat Al-Baqarah, if recited in a dwelling, no devil will approach it for three nights.