Does Apple watch have built in speakers?

Yes... for answering a phone call.

But not for listening to music. To listen to music you would need a bluetooth headset or speaker.

Yes but only for taking calls 🙂

unfortunately speaker seems to not be too loud.i wish it were louder. i wonder if they can do an update to increase it?

if a speaker is small then if software attempt to inc volume then it will just overload the speaker corrupting the sound