How to create a search box for other blogs?

You can with a Google search box (or Yahoo! or whatever), but doing so with WP’s built-in search engine might not be doable.

yeah but i want visitors able to search on my blog only. bc search engines won’t index every page and especially it’s a new blog so….

“Is it possible to create a search box on https://example.com to search https://blog.example.com“

Make sure the ‘action’ attribute value for your search form is the url to your blog:

<form method="get" action="https://blog.example.com/">