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.
Pushya - Pushya is nakshatra of nourishing and taking care of people without any selfish interests. It is closely connected with adoption and child care due to mythological story involved. For more information on Pushya Nakshatra, please check this link - https://www.astrosaxena.com/pushnaksh .
Cancer - As Pushya is a part of Cancer, Cancer sign and its representations become important. Cancer is 4th sign of Zodiac Belt, hence it represents the things represented by 4th house like Mother, Mother's Care, Emotions, Taking Care of Others and Nourishment etc. Cancer is consisted of 2 and half Nakshatras namely Punarvasu, Pushyami and Ashlesha. Cancer's lord is Moon, which again represents almost same things which Cancer and 4th house represents.
Moon - As Moon rules Cancer, Moon's position and dignity is important to know about the overall functioning of any planet in Pushya/Cancer.
Saturn - As Pushya is ruled by Saturn, Saturn's position and dignity will also have an important role in functioning and results of any planet in Pushya.
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 Pushya Nakshatra – Mercury is in enemy sign here but in friendly nakshatra. So dignity-wise, it is an average position. As Cancer and Pushya both are directly related with healing and health-care, Mercury in Pushya can show someone who is into medical field. Now, he can be a medical practitioner, counselor, healer, dealing with medicines or equipment of health-care etc. Basically, any business related with healing. As Mercury is also a teacher or counselor, Mercury in Pushya can show someone who is teacher in medical field. They can be naturally good at counselling or teaching people. At the same time, Mercury is in sign of Moon here. It brings the trait that they may find it difficult to make sensible decisions when it comes to themselves. They can be very good counselors for others but in their own personal life, they may take decisions purely on emotions rather than logic or any rationale. As Mercury also represents siblings and it can be a relationship oriented planet in many charts, it shows certain frustration in those relationships as it is in enemy sign or in Saturn's nakshatra. Overall, it is a great position for becoming a counselor or healer but it can have its own challenges in personal life.
Role of Moon – Moon's placement is important to guide Mercury in right direction, being Cancer's lord.
Role of Saturn - Saturn's placement is important to guide Mercury in right direction, being Pushya's lord.
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 Pushya. 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 Pushya can work in a chart.