You can know that there is a God. The Bible teaches that from the time of Adam and Eve, there has been a True and Living God who communes with the children of man, His children. And we learn that this God loved us so much that He sent His Only Begotten Son to save us from our sins. (John 3:16).
If we live according to these scriptures, we will know that there is a God, that He loves us, and that He speaks today!
And, as I said before, there is a way that we can test whether or not the scriptures truly teach the will of God. An ancient Book of Mormon prophet named Alma proposed an experiment to a group of people who wanted to know whether there is a God. He likened the word of God to a seed. And if the people had merely a desire to believe, they should plant that seed in their heart and nourish it. That is, they should begin living the Gospel of Jesus Christ. If it was a good seed, it would begin to grow:
Now, if ye give place, that a seed may be planted in your heart, behold, if it be a true seed, or a good seed, if ye do not cast it out by your unbelief, that ye will resist the Spirit of the Lord, behold, it will begin to swell within your breasts; and when you feel these swelling motions, ye will begin to say within yourselves—It must needs be that this is a good seed, or that the word is good, for it beginneth to enlarge my soul; yea, it beginneth to enlighten my understanding, yea, it beginneth to be delicious to me.
And God will manifest Himself to you, but you have to plant the seed. You have to keep the commandments. It’s only after you’ve planted the seed and nourished it through obedience that it will begin to grow. But it will grow.