When do you add the Truffles? Instructions never mentioned anything about it. Can you please elaborate more? Thanks

Traditionally & usually, in this dish the eggs are cooked, the truffles shaved over them quickly and the whole dish is served right away.
Sometimes, if you don’t have truffles, a truffle paste or butter is swirled in just at the end of cooking the eggs.
See recipes from Italy or France, or recipes from respected American chefs or cookbook authors.