I'd like to know if it's possible to take a screen capture of the satellite view of 'Maps' on my iPhone 6. It doesn't respond using the Home and Sleep buttons.
I'm not sure if you've jailbroken your iPhone or not, but default functionality for the home+sleep on all iPhones is to do a screenshot no matter the application that you are in. Signed apps from the Apple App Store are not allowed to override this built-in OS level functionality.
Your home button or sleep buttons might have a problem. Do they function normally on their own? If so, then it could be that you have an accessibility feature enabled which is overriding or interfering with this default behavior.
Just in case none of the above is the situation, my final thought would be that you aren't correctly engaging the screenshot combination. As a refresher or to clarify, you would hold the Home button along with the Sleep button at the same time. I have found that sometimes starting with the Sleep button can throw it off, so I start with the Home button and then quickly add the Sleep button a short moment later and then let go of all of it once the screen flashes (if audio is not muted you also get a camera shot sound).
Also, I'm assuming you know, but maybe you don't: you find your screenshots in your camera roll in Photos. I'm not sure if you were expecting it someplace else maybe. It doesn't put it into the clipboard if that's what you might have thought.
In case you might be looking for capturing a video of your iPhone screen (or alternatively you can do a screenshot), you can accomplish this by running QuickTime Player on your Mac (if you have one), connect the iPhone via a lightning USB cable, then go to File → New Movie Recording (⌥⌘N). From there you can see your iPhone's screen.