Recently, I was confronted with this question by a parent who was interested in unschooling her child: "What if I don't have the right answer?". She continued by highlighting children's inquisitive nature and her limited knowledge of things in general.
"I am highly passionate about my field," she said, "but what about the things I don't know? What if my child asks me about history, which I know very little about?"
The notion of the One Right Answer and the Summit of Knowledge is very much part of the school paradigm. In a school setting, the teacher holds the Right Answers, all of them, and each question just has one. This is possible because the information seen in the span of a lesson is controlled and pre-established.
There is no such thing in unschooling.
First of all, we break through the notion that there is just one answer. Sometimes there are none, sometimes there are many.
In unschooling, there is also no top down transfer of knowledge such as is attempted in a school setting, so sometimes the answer comes from the parent sometimes the answer comes from the child but it can just as easily come from a third party a book or the internet.
What is important is the process, the stimulation of seeking the answers. The feeding of the mind.
Whenever I don't have the answer, I will ask my child what she thinks. You will be surprised at the vast array of answers that come up. They might not al be 'true' but they will stimulate learning. Stimulating the way of finding answers is also much more important than just handing a clean cut answer to your child. And before you object to this method of learning, it's actually an established method of learning, called the Socratic method. After Socrates, who would entice his students to learning by answering each question with a question. Though I must admit I'm not as good as he was, I have to remind myself not to just answer the question every time. Then again, I was conventionally schooled.
Showing your child how to discern scientific information from hearsay, how to find the right references, discerning fiction from fact, that is what is important, and that is something you don't have when you're concerned of always offering the 'right' answer.
Furthermore, it is important that your child sees that you don't hold all the knowledge that you too are learning all the time. This may be a most stimulating notion. Monkey see, monkey do, also works when learning is concerned. If an unschooled child is confronted with an eternally learning parent, he too will wonder about the world, and seek out knowledge about the things that grasp his interest.
Unschooling requires a change of paradigm. If you can accept that answers will be found in due time, if you can grow that trust, then you're almost there.