What is the ruling on the zakat for a stagnant plot of land owned by the questioner, knowing that he is awaiting its sale to pay the price of another plot?

There is no Zakat (definition) on a plot of land intended for sale if it was not purchased with the intention of trading, because it is neither a trade good nor a self-growing asset. Fixed assets are not subject to Zakat unless they generate income, in which case Zakat becomes due on their income after the passing of a full Hijri year.