The first step is always the same: have hearing checked. Not because it is likely, but because without it everything else is guesswork. If hearing is fine, the second question begins — whether the child fails to respond always and everywhere, or only when absorbed in something else. Those are two different things.
In the first case the child hears and understands; it simply has a narrow beam of attention and cannot switch it — coming closer, touching and only then speaking helps. In the second case the sound arrives but does not connect to meaning; the name is just another sound. That is not disobedience or attention, but speech processing.
The symptom profile for toddlers covers nine areas including hearing, speech comprehension and attention, and shows which is weakest. Response to a name is exactly where these three get confused, and the questionnaire helps to separate them.