From the UX perspective, a survey should be visible but not distracting. When you decide where to display one, consider the website design. Be mindful of the elements of your site, like CTA buttons that you wouldn't like to cover up.
In terms of landing pages, analyze the conversions funnel and the analytics data to find underperforming sites or the sites with high drop-off rates. Trigger a website feedback survey there.
If surveys placed on those sites get low response rates, consider asking for feedback on the page just before those with high drop-off rates.
Alternatively, trigger a website feedback survey on the most vital pages for your business. These could be case studies, use cases, or pricing pages. Do so regardless of their performance. Even if the pages have satisfying conversion rates, there may always be some room for improvement.
Also, the landing pages communicating your offer are worth examining. Ask for feedback on their clarity. And find out if they answer all the questions your audience has.