Hi,
If you would like to add some analytics or similar code to your website, you have to use some kind of plugin for this.
I use this plugin for this purpose
https://wordpress.org/plugins/addfunc-head-footer-code/
You can search for this in plugin repository for more plugins.
the problem is that i need to locate where to add my code
i want to add it after a user use the contact module
where there is “thanks for contacting us”. thta page i want to use the code
but with jeasyjet contact module, there is no separate “thank you page”
If you need help with jetpack module, you can ask their support for it. I am not familiar with it.
I am not sure if jetpack contact form is able to do redirection after submission. Maybe some another plugin can extend jetpack form with this functionality or even better, search for more flexible contact form.
My suggestions
https://wordpress.org/plugins/formidable/
https://wordpress.org/plugins/ninja-forms/
https://wordpress.org/plugins/contact-form-7/