However, what if all you really want is to not require a registrant to have to keep providing their information repeatedly across your forms? Where the forms would simply pre-populate with the information they've entered previously on any of your other forms. That way they don't have to keep re-populating the form and you don't have to go through the more cumbersome approach of using the form population cloud component or web data lookups to pre-populate from the Eloqua record. For this use case, I highly recommend using the jQuery plugin StickyForms to achieve this.
StickyForms is one of the jQuery plugins I've developed and contributed to the jQuery community specifically designed not to lookup data, but simply remember it. It'll automatically re-populate any form on your website with data the visitor previously entered on any other form on your website, and it's incredibly simple to add to any landing page hosted in Eloqua (or any other hosting environment).
The full documentation of the StickyForms plugin and information about my other jQuery plugins can be accessed via the link below, but I also have a short-cut summary of the simple 3-step process to add StickyForms to your Eloqua landing page.
Full documentation and access to other plugins: RWSApps | StickyForms - Documentation
3-Step Process to adding jQuery StickyForms to your Eloqua Hosted Landing Page
Open your landing page, and copy the following code into the JS Editor of the Landing page. You can find the JS Editor by opening the Tools section of your landing page, clicking the far-right Page Snippet Tools tab, and then clicking the "Open JS Editor..." button at the bottom.
// Where rs-sticky-forms is the elqFormName
Replace the "elq-form-name" snippet in the code with the elqFormName copied in Step 1.
Save the landing page and load the form. Once you've submitted any form that uses StickyForms on the same sub-domain, the values will be automatically populated on any other form on the same sub-domain that uses StickyForms. For a full demo of the plugin in an Eloqua landing page, check out the example below.
Functioning demo: Eloqua StickyForms Example