You're not going to like the answer. Unless the dot is there, you just don't know. You have to know the word.
You know how in English you sometimes see a word in writing for years and never hear it spoken, and then you hear it spoken and it's pronounced very differently than what you thought? Happened to me with "segue". Who knew it was pronounced like "Segway"? It's the same with the ש in Hebrew. You just have to know how the word is pronounced. And it's usually better to assume sh. It's more common because all words borrowed from other languages with an s sound were written with ס.
I just wonder , but I may be wrong, if the pointing dots as you called them (they are actually the vowels) are there because normally you would pronounce a letter like that aleph as "a" as in the word "bat" but the 3 dots is the vowel that is pronounced "e" as in the word egg. There is also a vowel with 3 dots under each other at an angle like a french accent except under the letter which is pronounced as "oo" as in the word "boo". There is a vowel that you find at the beginning of a word which is 2 dots straight down which is pronounced like a short "i" as in the word "bit". There are another couple of vowels using the letters but I won't confuse you further!! Children are taught to read using the vowels but they are not usually used in modern Hebrew only in Hebrew used in prayers in the synagogue out of Israel.
I know what נקדות are, but Duolingo almost never uses them, yet here one is. Is it used in this word in modern Israeli writing, and if so, then why?; and if not, then why is Duolingo using it?
I realize now that it's to distinguish ‘רואֶה’ from ‘רואָה’, but I still wonder if ‘רואה’ always has dots in modern Hebrew or it's just Duolingo condescending to use them.
The simple answer is that there are no rules for when to use them. If you want to know how often Israelis use them, ask them if they know how to make them in their favorite OS/word processor. You'll usually get a blank stare, although there is a way. Newspapers and books will add them occasionally on specific letters when the word is unknown and they don't expect the readers to know how to read this. This is why Duolingo added this here.
The Hebrew academy proposed some years ago something called the seven-dot system of partial nikkud that would solve most ambiguities, but it was never widely adopted. So, no rules.