When I click "Apply to be a Registered OptiX Developer" it's redirrect to "surveymonk

When I click “Apply to be a Registered OptiX Developer” it’s redirrect to “surveymonkey.com”. wtf ?

Where I can download optix 3.5 and previous version ?

As the form clearly says, You need to fill up the Nvidia Optix survey to apply, the survey is done by surveymonkey.com.

When done, it will be reviewed, and if accepted, You will get an email with more infos!

Do I need to use the same e-mail in surveymonkey.com as in the optix 3.5 developer registration ?

Just use a valid personal non-temporary e-mail address under which you want to receive the download information.
It doesn’t need to be the same as the one under which you opened a developer.nvidia.com account, if that’s what you mean.