The head of Nike doesn't know how to make shoes, the CEO of Mars doesn't know how to make baked goods - yet they are both respected and successful leaders.
You don’t need have the answers to everything: you are not a domain expert in every area that comes under your remit.
Your strength is not to hold enormous amounts of knowledge, it’s to be a problem solver, to know where and how to find all the answers, or to to know how to surround yourself with experts and people who can help.
Saying you don’t have the answer isn’t a sign of weakness, but pretending you know when you don’t will backfire spectacularly sooner rather than later - at great cost to your credibility and authority.
In addiion, admitting you don’t know the answer to a question will pave the way for others to do the same, leading to a more open and trusting group.
Finally, asking others what they think should be done is a great way to motivate and empower a group. Your role is then to ensure that the solution is a good one.