I have found (at work at least) a good starting point can be to compliment people. If you notice something different (hair done differently, interesting jewellery, nice jumper, etc.), comment on it. Whether you like it or not is essentially beside the point; if it's different, interesting, or you haven't seen it before, tell them you like it or its interesting

There are a range of types of dementia, and they all look slightly different on scans of the brain (often MRI's) and might have different signs from blood or other tests that differentiates the types from each other.

The different types also effect people's function slightly differently, and both family history and just general life history can help with determining the type of dementia. For example, if someone is known to have had a history of alcohol excess they might be more likely to develop an alcohol related form of dementia so that might be the starting point for investigations.

Alzheimer's is the most common hence being the one most people are aware of.

The other main types are:

Frontotemporal dementia, which often develops slightly younger and can lead to quite significant personality changes and challenging behaviours (among other things).

Lewy Body dementia, which can often present quite similarly to Parkinson's disease.

Vascular dementia, which is often correlated with multiple strokes or other vascular (blood flow) changes to the brain. The functional impacts to a person can often depend on which part of the brain is most impacted.

Mixed dementia, which is essentially a combination of types.

But that isn't an exhaustive list and there are other less common types, and yes most of them have names.