Is “Dentists all over the world are telling their patients the same things. You must floss regularly” an example of Ethos and why

No. It isn't an example of ethos.

Explanation:

Ethos refers to an argument that's based on the credibility of the person that's making the argument.

Ethos simply means establishing the authority to speak on a particular object subject. It's the persuasion and the argument whereby the knowledge, good moral character and the credibility of the speaker is shown.

In this case, the example given isn't an example of ethos because dentists in this case is a broad term and therefore does not give credibility from a particular dentist or probably a dental research.

do you have a picture of the cartoon?

the present continuous is a verb tense which is mainly used to indicates that an action is in progress at the moment of speaking.  

it is formed using: person + verb to be (am/is/are) +verb + - ing form  

example: i am studying at this moment .

in addition, the present continuous is also used in order to express things that will or will not happen in the near future.

example: i am having dinner with some friends tonight.

the speaker sometimes   uses it   to express that an action is repeated and it causes irritation on the part of the speaker

example: my sister is constantly complaining about everything.