Sometimes libraries have dependencies on other 3rd party libraries. That is the case with the DallasTemperature library you're attempting to use. It requires you to also install the OneWire library. You may be able to get that from Library Manager or maybe you'll need to download it and then install that file. You might want to do a bit of searching for documentation of the DallasTemperature library to see if it specifies a certain version of the OneWire library for you to install. If you look at the DallasTemperature entry in Library Manager there should be a "More Info" link you can click on. That's a good place to start.