How do I open developer tools on iOS Simulator?

Open Safari and go to Preferences. Under the Advanced tab, at the bottom, you'll see "Show Develop menu in menu bar". Make sure that is checked like in the image below.

Once that is checked, you'll see a new menu bar item named "Develop" between "Bookmarks" and "Window" in Safari's menu. Under the Develop menu, select "Simulator" and then select the site you want to debug. A new window with the developer tools will then pop up:

Download https://developer.apple.com/safari/technology-preview/

Open the website you want on your simulator.

On "Safari Technology Preview", under

Develop > Simulator --- [SimulatorName] > select your website from the list.

If you are on a mac, press CMD + G while running the Simulator on XCode. This will allow you to Inspect element like you can on a web browser.

To hide the menu, press CMD + D.

It looks like the most accepted answer incorrectly assumes the asker is wondering about Safari Simulator, not XCode Simulator.