This is premium only feature, you would need to be on at least "Professional" plan.
If you are using old theme which doesn't support Online Store 2.0, there is no easy way to show specific FAQs on specific products.
If you are using Online Store 2.0 compatible theme, then follow this tutorial

Following example shows how to show FAQs on all products detail page.

1. Visit your stores admin panel.

2. Click on "Online Store" > "Themes" > "Action" > "Edit Code".

3.   Open "product-template.liquid" file which you can find under "Sections". Add following code snippet at appropriate location.

<div id="ef-faqs-plus-app-content"></div>

If you wish, you can also use categories "Embed code" here which would show only FAQs from that category instead of all FAQs. Visit categories section in app to get embed code.

On default Shopify themes, it's located on line 338.

Location can change depending on theme you are using. Please contact your theme developer if you are unsure about where to place. If they can't support, feel free to reach out to us.

If you wish to show these FAQs only if product belongs to certain collection then please refer to code snippets mentioned here.

4.  Save page and you should see FAQs on your product details page.

If you would like to show FAQs on pages other from product detail page, please contact your theme developer as they can help you quickly as they exactly know the location. If they can't support you, feel free to reach out to us and we are more than happy to help.

5. Enable embed FAQs feature. Please follow these steps to make sure feature is activated.

Design and Settings > General > Show FAQs on other pages > View Settings > Activation > Activate.

After activation, you should start seeing FAQs at appropriate place.