You can use template sensors to create sensor entities from the device_tracker entity attributes. However, I don’t believe you’ll be able to ask Google Assistant where your pet is (seems to be a Google Assistant limitation). If you visit the Home Assistant Google Assistant documentation, you can see that sensor entities can be exposed to Google Assistant, but not device_tracker entities. If you were to create a template sensor which uses the current state of the device_tracker entity, you’d be able to expose said sensor to Google Assistant, but I don’t believe Google Assistant would tell you the state of that sensor if you were to ask it.
To get around this:
Create a template sensor that takes in the device_tracker entity’s state and puts it in a sentence, which the TTS service will use. For example “The cat is at X” with X being the device_tracker entity’s state.
Then create a script in Home Assistant that calls the TTS service using the state of the sensor mentioned above. Only problem is, if you have multiple Google Assistant devices, you won’t be able to specify TTS to run on the particular Google Assistant device that you asked. If know you’re only going to be asking a specific Google Assistant device where your cat is then you can have the script call the TTS service on only that specific device. If not, you could have the TTS service run on all the Google Assistant devices in your home.
After creating the script you’ll need to expose it to Google Assistant. You won’t see it in the Google Home app- Home assistant scripts are exposed as “scenes” in Google Home.
You would then create a routine in Google Home that runs the “scene” (Home Assisstant Script) when you ask Google Assistant “Where is the cat”.
I’m not sure this will be of any use if you’re trying to get exact coordinates for your car as this would only use the state of the device tracker which takes on a value corresponding to the preset safe spaces that you defined in the Whistle app.