Yes dogs do know that you love them and they can let you know that they love you.
When a dog loves you they will usually show affection by wanting to be near you or licking you in the face or just snuggling up too you and want to be petted.
Dogs can also sense when you don't love them so you need to show love for your dog for them to love you back.
Some people get dogs and then just leave them alone outside most of the time and that's not what they are meant to do.
Instead dogs should be loved and brought into the house with you to be around you.