Let’s look at important things here –
Mercury - Mercury represents communication skills, marketing, calculative ability, younger siblings, hobbies, skills with hands, intelligence, quick decision making, logical thinking, youthfulness etc.
Jyeshtha Nakshatra - It is a nakshatra of feeling better or higher than others. It represents orderly and justifiable people. It is the most closely connected nakshatra with occult and mystic. For more info on Jyeshtha Nakshatra - https://www.astrosaxena.com/jyeshtnaksh.
Scorpio - As Jyeshtha is a part of Scorpio, Scorpio sign and its representations also become important. Scorpio is the 8th sign of zodiac belt, hence it represents the things and energy related with 8th house of horoscope like Sudden Events, Secrecy, Dark World, Occult Science, Research, Inheritance, Serving Others, Taxes etc. Besides these things sign of Scorpio also represent transformation, means changing the whole nature upside down. This is one sign which is favorite of every Astrologer, because it has maximum secrets, so every astrologer gets maximum scope of researching. This is sign about which no one can tell with precision that what will happen to the planets in it, as it is sign of secrecy itself. Wherever Scorpio falls in your chart, you may have had biggest challenges in making things related with that house more stable. Scorpio is also one of those unique signs which has 2 rulers, i.e. Mars and Ketu. In Western Astrology, Pluto also co-rules Scorpio. All this makes Scorpio a chaotic sign. Scorpio consists of next set of 2 and half nakshatras, i.e. Vishakha, Anuradha and Jyeshtha.
Mercury - As Mercury rules Jyeshtha, Mercury's position and dignity is important to know about the overall functioning of any planet in Jyeshtha.
Mars-Ketu - As Mars-Ketu rules Scorpio, their position and dignity is important to know about the overall functioning of any planet in Jyeshtha/Scorpio.
Houses Involved – Also, we can’t afford to forget the houses involved as a planet can be ruling different houses and sitting in different house for every person as per ascendant and planet’s position. To know overall affect, we have to consider the houses involved as those areas of life are being impacted.
Interpretation of Mercury in Jyeshtha Nakshatra – Now, Mercury is in enemy sign ruled by Mars and own Nakshatra. So, it is kind of average position again where planet is strong at nakshatra level but weak at sign level. I will write an article separately on how to interpret planets in such position. Common theme around Mercury, Scorpio and Jyeshtha is Occult. Jyeshtha is closest nakshatra to occult and research oriented subjects. As we know, Scorpio is the main sign of occult. Mercury remains karaka of Astrology. So, this position can give extreme interest in occult side of life or in any kind of research oriented work. As Mercury represents business, business related to occult is best for them. They can be very fair and justified in their business. They can also be very ambitious or find ego satisfaction through the success of their business.
At the same time, it can be a difficult position for relation as Mercury is not only in enemy sign but Jyeshtha is Gandamool nashatra which also has Gandanta degrees. So, it can bring lots of instability on relationship front.
Overall, an excellent position for being an occultist.
Role of Mercury – As Mercury will be in own nakshatra, being Jyeshtha lord, we need not to see Mercury position separately.
Role of Mars-Ketu - Mars-Ketu placement is important to guide Mercury in right direction, being Scorpio lords.
Other Factors – And of course, we need to consider conjunction, aspects, house lordship, house position and dashas etc to know the exact results of Mercury in Jyeshtha. So, we always need to take a holistic view of chart rather than just 1 planetary position.
Conclusion – So, this is how I see Mercury in Jyeshtha can work in a chart.