Let’s look at important things here –
Mars - Mars represents our will power, courage, ability to take actions, aggressive nature, anger, our fighting ability, brother, male friends, a boy friend for a girl, a soldier, an athlete and real estate etc.
Dhanishtha Nakshatra - It is a nakshatra related with wealth, luxury and lavish life. It is also a nakshatra related with music. Also, it is a nakshatra of celibacy. Please check this link for more info on Dhanishtha Nakshatra - https://www.astrosaxena.com/Dhannaksh.
Capricorn - As Dhanishtha is part of Capricorn sign, Capricorn and things represented by Capricorn are also important here. Capricorn is the 10th sign of zodiac belt, hence it represents many things related with 10th house of horoscope like Law and Order, Government, Authority, Organisation, Discipline etc. Besides it also represents World outside your home and people, Fear and Anxiety etc. Capricorn is consisted of next 2 and half Nakshatra, i.e. Uttar-Ashadha, Shravana and Dhanishtha. Capricorn is ruled by Saturn and that's why it represents Fear and Anxiety.
Aquarius - As Dhanishtha is also a part of Aquarius sign, Aquarius and things represented by Aquarius are also important here. Aquarius is 11th sign of zodiac belt, hence it signifies the things and energy related with 11th house of horoscope, such as Gains, Desires, Hopes and Wishes, Large Organisations, Network Circles etc. Besides this, Aquarius also represents Scientific Thinking & Research, Uplifting the Society, Higher Goals & Rewards for all. Aquarius is made of another set of 2 and half Nakshatra, i.e. Dhanishtha, Satabhisha and Purva-Bhadrapada. Aquarius Lord is Saturn & Rahu.
Mars - As Mars rules Dhanishtha, Mars's position and dignity is important to know about the overall functioning of any planet in Dhanishtha.
Saturn & Rahu - As Saturn rules Capricorn & Aquarius and Rahu co-rules Aquarius, their position and dignity is important to know about the overall functioning of any planet in Dhanishtha/Capricorn and Dhanishtha/Aquarius.
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 Mars in Dhanishtha Nakshatra – We can say that Mars is strongest here especially in Capricorn portion of Dhanishtha. It is because Mars is exalted in Capricorn and it is in own nakshatra. Mars is the only planet which is exalted in its own nakshatra. So, Mars in Capricorn/Dhanishtha can make someone very courageous, strong on will-power and action oriented. They can be very ambitious and looking for high authoritative positions. They will also be ready to work hard and tirelessly for that. It is important for them to get into authoritative positions else their ego will not be satisfied and they will feel like an under-achiever. They can work in government departments like Army or Police but wherever they are working, they would be in authoritative position. They will work hard to get all the luxuries and conveniences of life which Dhanishtha promises. Only major difference in Aquarius/Dhanishtha is that they may like to get the same authority with an idea of serving people. Also, Mars in Aquarius/Dhanishtha person may get this authority through entrepreneurship. So in Capricorn section, person wants authority for his own ambitions and ego satisfaction whereas in Aquarius section, person will look for authority so that he can serve others. If Mars becomes a relationship planet for the person being 7th or 5th house lord or darakaraka then this position can make relationships very troublesome. Overall, a great position to gain authority but can bring major relationship conflicts.
Role of Mars – As we are trying to interpret Mars, we need not to see Mars's position separately as Dhanishtha is ruled by Mars only.
Role of Saturn & Rahu - Also, Saturn-Rahu placement is important to guide Mars in right direction, being Capricorn & Aquarius 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 Mars in Dhanishtha. So, we always need to take a holistic view of chart rather than just 1 planetary position.
Conclusion – So, this is how I see Mars in Dhanishtha can work in a chart.