To get an idea of what the visitors are looking on the site, you may want to capture search keywords and pass them along to an Adobe Analytics variable. Before doing this consider a few best practices:
1. Remove trailing spaces
2. Convert the query into lowercase
Make sure that a single search is tracked once (avoid duplicated server calls).
In addition to a prop/eVar variable, populate an event on every search — this will give you a metric showing the number of searches. Alternatively, configure a calculated metric in Analytics UI.