My iPad 2 have the 9.3.5, how can I update to 9.3.6?

If you have a WiFi only model, you can not, nor do you need to.

Update your iPhone or iPad software to avoid issues with location - Apple Support

1. This update is unnecessary if you don't have the cellular version of iPad, but strongly advised if you do.
2. If you have tried Software Update and it doesn't install (whirling grey roundel), go to step 3
3. Try signing out from your Apple account using your Apple ID and password (if you don't have it anymore, then you might need to contact an Apple store). The Sign Out option should be under Settings/iTunes & App Store, at the bottom of the list. Keep the Apple ID etc handy for when (or if) you need to sign back in. Go to Settings/General/Software Update and click Install. It should now install without problem; just don't expect it to complete quickly - be patient. After a reboot (white Apple logo and thin white progress bar), you will come back to the home screen and ios 9.3.6 should be installed ok.