Is Zakat obligatory on a plot of land that was purchased two years ago, given the hesitation between building on it for residential purposes, selling it to buy a better plot, or holding onto it for future need, and in this case, is it considered an investment, savings, or a future dwelling?

There is no Zakat (definition) due on land unless it is a trade commodity. The mere intention to sell it when needed does not make it so. Zakat becomes obligatory on its price only after it has been sold, a [lunar] year has passed, and it reaches the Nisab (definition) either by itself or when combined with other money.