Isolated, the Jack of Diamonds represents the postman or, better said, the messenger. It also symbolizes a young soldier or an unfaithful servant (assistant, employee); sometimes a young blond man, traitor and of bad morals.
If the consultant is a young man, it is the announcement of new lovers.
If it is a young girl or a single woman, it is the certainty that, soon, a suitor will make himself known; he will be blond and pretty boy.
If, on the contrary, the consultant is married, he will soon learn of a somebody’s else marriage; but this card, surrounded by it, has many and varied meanings.

The Jack of Diamonds with a
Spade ♠: Treachery, infidelity.
Heart ♥: Certainty of marriage and news of birth.
Diamond ♦: Young risk-taking man, adventurer of misconduct.
Club ♣: Somebody will ask to borrow money from you.

Having on the left a
Spade ♠: A dark man you have every reason to fear.
Heart ♥: Love. Letter coming soon.
Diamond ♦: Null card.
Club ♣: Money that will be lost. Theft.

EXCEPTIONS.
The Jack of Diamonds, with the
King of Diamonds: News from a young adventurous man.
Between two sevens: News of a pregnancy.
Touching the Ten of Diamonds: Distant journey. (The other card touching it becomes null and void.)
Touching the ace of Clubs: News of an inheritance. (The other card touching it becomes null and void.)
Between two face cards: deceit, treachery, infidelity.
Between two aces: The Jack of Diamonds says nothing; he is absolutely silent.

The King of Diamonds sometimes symbolizes a soldier, or more generally – a man in a dangerous occupation, exposed to risks of injury or violent death (policeman, firefighter, roof-tiler, aircraft pilot and similar professions with elevated risks). For a young woman or a divorced woman, the isolated card means a proposal for marriage from a man in a dangerous occupation.
It also represents a blond man, self-important, haughty, fearsome, deceitful; in a word, a bad man.
It is one of the cards whose meaning depends mostly on the cards surrounding it.
So the number of its exceptions, i.e. special cards that give it a different meaning, is quite varied, as you will see below.

This card announces, having on the right a
Spade ♠: Naughty, quarrelsome man, whom you should be wary of.
Heart ♥: A beginning of a relationship with someone, who is not good for you. If the consultant is married: new acquaintance not to be frequented.
Diamond ♦: Flatterer of which we have everything to fear.
Club ♣: Somebody will try to steal from you.

Having on the left a
Spade ♠: Obstacle in your projects by a blond man.
Heart ♥: Serious suitor. If the consultant is old or married: loving and honest man.
Diamond ♦: Quarrel.
Club ♣: Advantageous offer by a blond man.

EXCEPTIONS.
The King of diamonds placed between two face cards, whatever they may be, means: Disunity, confusion.
With the Jack of DiamondS: News from a young man in a dangerous profession.
Between two SpadeS: Rivalry.
With the Queen of HeartS: Love of a soldier. For married or elderly people: Upcoming acquaintance of an honest man, military.
Having an ace on the right, the usual meaning of the card on the left is nil. Instead, this announces, regardless of the colour of the card on the left – upcoming trip away related to some danger or a man in dangerous business.
The King of Diamonds, between two diamonds, announces the visit of a man from out of town.

This happy card, taken in isolation, means: Serious blond man who will be your protector.
From this honest man, you will only receive excellent advice; he will be a sincere friend to you.
His loyalty will be a sure guarantee of his good intentions towards you. Listen to him in everything; he will guide you on the right path and even, if you are troubles, his kindness will not fail you.

The King of hearts having on the right a
Spade ♠: A married blond man means you well.
Heart ♥: He will help you to find someone special for you. – He will do you a great service.
Diamond ♦: Is on his way to see you.
Club ♣: Will send you money soon.

Having on the left a
Spade ♠: You will be taken care of.
Heart ♥: Guaranteed protection of your interests by a blond man.
Diamond ♦: Upcoming trip on business of interest; a loyal man will help you to carry out this business successfully.
Club ♣: Protection of a very rich blond man.

EXCEPTIONS.
With the Queen of Hearts: Advantageous relationship or marriage. – More abundance.
Between two cards of the same value: Plans for building a close relationship with somebody.