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.
Krittika - It is nakshatra of criticism, cutting things, surgeries and bloodshed. Also, it is nakshatra of child care, secrecy, research, protection and foster parenting etc. It spreads from Aries to Taurus. It is ruled by Sun. For more info on Krittika, please check this link - https://www.astrosaxena.com/kritnaksh .
Aries – As Krittika is part of Aries, Aries sign and its representations become important here. Aries is the 1st sign of zodiac belt, so it represents the things and energy of 1st house of horoscope like Self, Personality etc. Besides that, Aries is the sign of our individuality, our aggression, our actions, our competitive ability etc. Aries is ruled by Mars and it is consisted of 2 and half Nakshatras named Ashwini, Bharani and Krittika.
Taurus - As Krittika is also a part of Taurus, Taurus sign and its representations become important here. Taurus is the 2nd sign of zodiac belt, so it represents many things related with 2nd house of horoscope like, Hoarded Wealth, Assets, Savings, Finances, Luxuries and Liquid Money. All in all a sign related with luxuries and all the conveniences of life. Taurus is consisted of 2 and half Nakshatras, i.e. Krittika, Rohini and Mrigshira. Taurus' lord is Venus.
Mars – As Mars rules Aries, Mars’ position and dignity is important to know about the overall functioning of any planet in Krittika/Aries.
Venus – As Venus rules Taurus, Venus’ position and dignity is important to know about the overall functioning of any planet in Krittika/Taurus.
Sun – Likewise as Sun rules Krittika, Sun's position and dignity is important to know about the overall functioning of any planet in Krittika.
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 Krittika Nakshatra – Now, Mercury is in Krittika Nakshatra which is ruled by Sun. Dignity-wise, Mercury is in nakshatra of friend and in Taurus also, Mercury will be in friendly sign. Only issue is when Mercury is in Aries as its lord Mars is enemy to Mercury. So, when Mercury is in Krittika/Aries, these people need to be very careful with their communications. They can be very critical and sharp with their speech which can create enemies for them. Likewise, they need to be careful against negligent/rash driving as it may cause accidents. At the same time, they can be very good critics by profession. It includes being an editor too. As Krittika is closely connected with child care, they can be working in any business or communications related with child care etc. In Taurus section, they can be good in financial side of business and can be very calculative/practical about wealth matters. Here, communications can be pleasant one. Mercury related relations can suffer due to ego conflicts. They can be good at Spying and business related with weapons too.
Role of Mars – Mars's position will become important in functioning and results of Mercury in Krittika/Aries as Mars rules Aries.
Role of Venus – Likewise, Venus's position will become important in functioning and results of Mercury in Krittika/Taurus as Venus rules Taurus.
Role of Sun - As Sun rules Krittika, its position is also important to finally decide about the results of Mercury in Krittika.
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 Krittika in either of the signs. 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 Krittika can work in a chart.
Hope this helps. Please post any comment or query you may have.