My dad does not understand how the clock works. Any suggestions?

Cagary, is there a reason for your Dad to know how to tell time at this stage of his life? If not, then don't fret about it.

Got an 'atomic clock (advertised on Fb) gives the day, date and time - first thing he sees upon waking. Put a scarf over it at night - pretty bright in a bedroom. And it resets if there's a power outage.

My Mom could no longer read a regular clock but she did OK (not great) with a digital wit large numbers. That glowed in the dark.

As said its progression of the desease. He can no longer tell time. Like he will forget how to use a phone and a remote. Will forget how to read. Will forget how to use a stove. As the desease progresses part of the brain dies.

That is part of the progression of dementia. The same thing happened with my father. One day he could tell time, the next day he had trouble and soon after he could not at all.

A little more info would help.
For you the clock is but 1 test of many on what is called the MME or Mini Mental Exam. It is the start of diagnosing dementia.
If your dad was given an MME and he did not draw the clock properly that is but 1 indication that he may be having problems. (Have no idea what exam they will include when people no longer know what an analog clock looks like!)
Further testing should be done to determine how advanced his dementia is and if possible what type of dementia he has.
Dementia is the general term and there are many forms of dementia all with their own symptoms and problems and a person can have more than 1 type of dementia at the same time.
If you can provide more info either updating your profile or adding info here it might help give you more answers.

Is this a question, or a statement? Are you referring to the clock that one is asked to draw during a cognitive exam? How old is your dad?