Soy lecithin is an emulsifier additive. In this particular case, it's derived from soy beans. Lecithin occurs in other products too such as egg yolks.
Light soy sauce refers to the level of carmelization of the sauce, not the sodium or calories. It is the most common soy sauce.
Sofrito varies a bit depending on which lcountry you're talking about, and even within the same countries. In Italy, Marcella Hazan describes it as cooking onions and parsley as the beginning of many dishes. Lidia Bastianich refers to it more as like a mirepoix including carrots and celery as well as the onion
It changes again in Spain and even more in Latin countries of the Americas, where it includes peppers and cilantro and garlic.
But in general, it is a mixture of chopped vegetables that form the cooking base for the recipe.