That will depend on your nationality. Irish and British citizens can travel between Ireland and Britain without needing a passport, though many will bring their passport with them anyway. If you are not from Ireland or Britain, then you will need a passport, and may even need a visa.
If driving, no you do not need a passport to go from Northern Ireland to Southern Ireland, only enough money for the toll booth.
I don't think you need one if you're flying but I'm unsure.
not if you are a UK citizen - but some airlines require everyone to have a passport for travel purposes
No.
No
Yes they do need a passport for Northern Ireland
Not if they're travelling from Northern Ireland, but from anywhere else he/she does.
If you are travelling from the USA to Northern Ireland, you need a passport to go there. You probably will also need a visa to enter Northern Ireland but you can find this out if you look up the British government website.
No.
only if you are going to Northern Ireland, you need a passport to travel between England and Ireland.
Yes, your passport.
Yes, you need your passport.
last year when i went to southern ireland even though i was born there i was asked for a passport
No.No.No.No.No.No.No.No.No.No.No.
Yes - you will need to show it on arrival in Prague and to leave Northern Ireland.
Theoretically no as Northern Ireland is part of the United Kingdom. However, acceptable photo ID is required to board an aircraft so if your journey involves flying, you will need ID and a passport is the most acceptable form of ID.
No, Belfast is in Northern Ireland which is part of the UK - you don't need a passport to travel from one part of the country to another.