If you're concerned, try talking to your child's doctor or a speech therapist. Almost 3 year olds will often still have trouble stringing a sentence along and holding a proper conversation but if you're concerned, early intervention is always best! There's also a workshop by this person that's pretty good https://www.instagram.com/raisinglittletalkers?igsh=MTZrd210bGpxd3huYw==
I think it's tye amount of words they should be able to say by now, and stringing short sentences together instead of just 2 or 3 words. Plus the forming of the words and if they speak at the back of the throat or more the front of the mouth.