My dad was born in another country and bought real property before immigrating to America. After he moved to America and became a US citizen, he maintained ownership of the foreign property. He now wants to sell the foreign property for a good profit and bring the money over to the US.

Is any of this a taxable event?

If so, how can he avoid taxation or minimize it?

Yes, it IS a taxable event, because U.S. citizens pay taxes on ALL world-wide income.

However, he will pay the tax at the capital gains rate, which is either 5% or 15%, so the tax has already be considerably minimized.