Is this right?

Complete subject: Sniffer dogs
Simple subject: dogs

Sniffer dogs trained to detect drugs, blood, and explosives can help solve crimes and save lives.

Your simple subject is right.

The complete subject:
Sniffer dogs trained to detect drugs, blood, and explosives

The participial phrase modifies dogs and is part of the complete subject.

Yes, you are correct!

The complete subject of the sentence is "Sniffer dogs." This is the noun phrase that includes all the words that describe or modify the subject of the sentence. In this case, it refers to the specific category of dogs that are trained to detect drugs, blood, and explosives.

The simple subject, on the other hand, is the main noun within the complete subject that the sentence is primarily about. In this sentence, the simple subject is "dogs." It refers to the general category of animals.

So, to summarize:

Complete subject: Sniffer dogs (referring to the specific category of dogs trained to detect drugs, blood, and explosives).
Simple subject: Dogs (referring to the general category of animals).