Is zakat obligatory on land purchased with the intention of preserving wealth, with the possibility of building on it, renting it out, selling it, or inheriting it? And how is its zakat estimated if it is obligatory?

Answering your question, the land that is bought with hesitation about selling it, keeping it, building on it, or leaving it for heirs, is not considered a trade asset and therefore, no zakat (definition) is due on its value. As for the money with which the land was bought, if it reached the threshold (nisab (definition)) and a year (hawl) passed over it before the purchase, then zakat is obligatory on it and is not waived by the purchase of the land. However, if the land was bought before a year passed over the money, then no zakat is due on it.