Those concepts are very easily explained. Consider yourself. Everything that is a part of your is part of your personal space. If you can it aside it may belong to you but it is not a part of you. Now, is there any place you are where it can be said you are not? The answer is No. Whereever any part of you is you are there. So, in terms of your personal space you are omnipresent. However, your component parts are not omnipresent because your brain is not where your feet are. But you are whereever your brain, or your feet, or your hands are. The same with omnipotence. You have power over every part of your body but no part of your body has direct power over the other parts of your body. In terms of your personal space you are omnipresent. You are omniscient in terms of your personal space and this demonstrates that omniscience is not about knowing detailed facts but having a full understanding of oneself. The only reason why you think you don't know all about your body is because you are considering what your brain knows, but your brain is not you, it is only a part of you. God is omniscient but He does not know every detail that you will do tomorrow. However, he does know everything you are capable of doing and cannot be taken by surprise.
Now, think of the Creator of the universe who, by definition, must occupy all time and space. There is nowhere in the universe that He is not because there is nothing outside of Him.