If Jesus knows what will happen, and he lets us control (ourselves), how does he know (what we will do)?
A good question – which by the looks of how it was written likely came from a young person. Thus, I will attempt a very simple answer for it – which is not easy to do, but here goes….
To answer this question (which is about God more than it is about us or our choices), it helps to think about “who” God really is. In thinking about who God is, it helps to begin with what is known about Him, or what we call His “attributes,” in order to understand His life in relation to our human lives. One of the attributes of God is that He is “all-knowing,” (or, to use another word, He is “omniscient”). To say that God is all-knowing is easiest to understand when thinking also of how God is also “all-present,” which means that everything that you and I might think of as in the past, in the present, or in the future, God is able to see as one “eternal” moment. In other words, every moment in God is one single moment – there is no past nor future; there is only the “present” that includes all time.
Aware that God sees all time as one, we can say that God is therefore “outside of time.” Even though His being outside of time is no easy thing for us to understand in its own way, to remember that God sees all as one present moment does help if we can think of both His seeing all time as present together with how He sees all that you and I are going to do (both good acts and sins) without taking away our ability to choose. This is because God allows all things that happen to happen in their own way. Likewise, by allowing us to make our own choices, God is making it possible for us to love Him (which is a choice). If we did not have the ability to choose, we would not be able to choose to love God or anyone else; we would only do what we were made to do by someone else, just like a computer only does what the person who built it and is using it only can do what it is told to do by the builder and user.
Therefore, because God is both all-knowing and allows us to have our freedom, it is important to practice always making the choices that lead us to God, aware that when we do not make good choices, God is still working for our good (by giving us such good things as the sacrament of reconciliation), so that we can keep growing toward living the way of life that will bring us true happiness – which is to live in the life of God forever in heaven.