If there is no wifi connection then the book will not download. You could get around this by connecting to your computer with a USB cable and downloading there instead.
For the device with the wifi problem, what have you tried so far?
Have you tried pressing and holding the power button to turn it off, then wait a few minutes and turn it on again?
Have you tried connecting to different wifi networks?
Are you getting an error message when you try to connect?
It is not possible to track the location of a Kindle. You can check if it is still in use by reviewing your account and see if any purchases have been made.
You should then immediately deregister it to prevent any purchases being made on your account. Go to http://www.amazon.com/myk and then Manage Your Devices to do this. That way no one can buy anything on your account and run up a huge bill.
You should also contact Kindle customer service ASAP. They can blacklist the device so that no one else can register it to their account. If it's already been re-registered to someone else before you contact them they can't do anything. They have no way of tracking a device.
Your satisfaction is my priority;
Kindly take a moment to rate my service 5 stars at the top of your question page so I am rewarded for my time; tips appreciated :)
You can always reply back at any time if you need any further assistance at all.