The two verses (Genesis 42:1-2) give no information about where Jacob came to know that there was grain in Egypt, but we do know: he saw something that his sons did not see.
What do you see that others do not see? Where has God already spoken to you about the future, but it still seems too big and impossible? These can be prophecies, but also insights from your conversation with God. If you have a vision, write it down if you haven’t already. This is very important! You should treat the piece of paper with your vision like a personal treasure that God has given you. If you have not yet received such a vision from God – it is not bad! You can pray for it!
When? Now! Give Him space to speak and expect Him to speak! Maybe you will receive your vision now!