It may be noted that:
With between 14.5 and 17.4 million adherents worldwide, Judaism is the tenth largest religion in the world.
It is believed that the present world population in 2018 is about 7,600,000,000.
Therefore, the larger estimate of the Jewish population is about 0.00228 of the total world population.
So one person out of every 436.78 should be Jewish. So how many total characters are there is Star Trek? Eliminating extraterrestrial characters, how many characters are there in Star Trek?
The 2016 estimated population of China is about 1,403,500,365 people, or about 0.1846 of the estimated world population in 2018 - one person out of every 5.417. Do 0.1846 of all Star Trek characters seem Chinese?
The 2016 estimated population of India is about 1,324,171,354 people, or 0.1742 of all the people in the world in 2018 - one person out of every 5.740. Do 0.1742 of all Star Trek characters seem Indian?
These two examples show that while Star Trek may be better than most American shows in depicting the diversity of the world population, the cast of Star Trek characters is far less diverse than the world population in the 20th and 21st centuries.
Since Jews mostly look like European or Mediterranean people, though there are Jews looking like members of every human race, and since most most actors cast in Star Trek productions look like European or Mediterranean people, telling Jewish characters apart from non Jewish characters would be difficult without religious or cultural references.
And only a small percentage of Star Trek characters refer to their ethnic, national, religious, or cultural backgrounds.
And I point out that in TOS, and to a lesser degree in other Star Trek productions, alien planets often had populations that looked like Earth Humans, and in fact usually looked like "white" or "Caucasian" Earth Humans. And since there are a number of planets in the United Federation of Planets with alien populations, It is probable that many of them have populations that look like Earth Humans even though those planets weren't colonized by Earth. Thus the Federaton should be full of people who look like "white" or "Caucasian" or other Earth Humans but are more of less native to those planets and not descended from colonists from Earth. Human looking people who probably don't share cultural, linguistic, or religious practices with Earth Humans.
So how can you tell which random Human looking characters actually are Earth Humans and which are aliens who merely look like Earth Humans? How can you estimate the percentage of characters who are Earth Humans as opposed to merely looking like Earth Humans?
If many of the Star Trek characters who look like Earth Humans are aliens who merely look like Earth Humans and have cultures different from any Earth cultures, the proportion of Jewish characters among Star Trek characters would be even lower than it would be if all Human-looking characters actually are Humans.
Therefore, I do not think that there are statistical grounds for considering Jewish characters to be under represented in Star Trek, nor do I consider Jews the first group that people should worry about being underrepresented in Star Trek - they should be more like number 100 or something on the list of underrepresented groups.