How can my apple watch receive notifications if bluetooth is disabled on my iphone?
Source.

Your Apple Watch can use both bluetooth and wifi to communicate with the paired iPhone.


  To enjoy every feature on your Apple Watch, you need to turn on Wi-Fi
  and Bluetooth on your paired iPhone. Swipe up on your iPhone to open
  Control Center. Then make sure Wi-Fi and Bluetooth are on.
  
  Your Apple Watch uses Wi-Fi and Bluetooth to communicate with your
  paired iPhone, switching between connections as needed:
  
  
  Your Apple Watch uses Bluetooth when your iPhone is near, which
  conserves power.   
  If Bluetooth isn’t available, your Apple Watch will
  try to use Wi-Fi. For example, if compatible Wi-Fi is available and
  your iPhone isn't in Bluetooth range, your Apple Watch uses Wi-Fi.