Question: A friend of mine who has water-treatment engineering degree recently moved to another country but struggles to find a job in his field. Because he did not want to stay at home unemployed (and because stealing food is not an option), he took a minimum-wage job (salesman in a small shop) that has nothing to do with his skills or even experience.

While I believe there is no shame for him to do that, I'm still not sure what to advise regarding his public LinkedIn profile and/or resume:

Should he mention the low-paying, unrelated job ? Is there any drawback in doing so ? Any drawback in **not** doing so ?

Answer: 
One advantage of mentioning the current unrelated job is that it shows that you are employed in city X. Instead of showing that your current job is in another country, or that your most recent job ended last year. 

It also shows that you have the necessary work permits for the country where you are looking for a job.
Avoid mentioning jobs that *may* hurt your overall job chances. Generally speaking, this is great "add-on" information that an interviewer can elicit from you("Have you ever taken a service-sector or low-paying job, to make ends meet?" - INSERT\_STORY )
.

But I would not put fast-food jobs on a page with more professional stints. 

It simply does not make sense. Again, bring it up in an interview to show your grit perhaps. But I generally don't see the point

LinkedIn, being a public "profile" , should focus on overall picture