How many carat of diamond worth one trillion dollar?

It would depend on the carat weight, the colour, the cut and the clarity of the stones to achieve this dollar amount.

There have been a few auction sales where single diamonds have been sold for US$15-30 million. The reason these stones sell for so much money is because they are so rare.

If, for example, you could find more stones of this quality, a single stone being worth $30 million, you'd need more than 30,000 such stones.