If you're speaking of the Middle Ages, depending on just when you mean-- many "Kings and nobles" might not be able to read religious texts in any language, not Latin and certainly not Hebrew. By and large, the people who hated Jews knew little about them; it takes an odd confluence of ideas to produce someone who is expert in what they revile. Their "magicians" and religious counselors were far more likely to read Hebrew and Arabic texts in translation than in the original.

Of gentiles with an interest in reading Jewish material, you're usually talking about a little after the "Middle Ages" -- quite a few Protestant scholars do. The Old Testament had been translated by Greeks like Saint Jerome, who knew Hebrew, but he lived in the 4th Century -- knowledge of both Greek and Hebrew would have been relatively common in late antiquity, but becomes rare after the fall of Rome.

If you were looking for one place where scholarly knowledge of Hebrew met a reputation for mystical and magical inquiry, that place would be Toledo in Spain. While tolerated at one time, you can imagine that this may have been fuel for the later Inquisition, and one can find reference to would be magicians and astrologers reading Arabic and Hebrew texts, but not in the original, translated into Latin by Muslims and Jews, typically.

As a center of learning, Toledo had a considerable reputation in the Middle Ages. Arabic and Hebrew works were there translated into Latin. It is this that gave Toledo a reputation for being a city of magicians and sorcerers. Legend has it that the Dominican saint Aegidius went there at the instigation of the devil to study magic.

One can identify late medieval scholars who could read Hebrew-- a notable one would be Roger Bacon,the 13th century philosopher who often gets called "the first scientist". Bacon was methodical in his reading, and while he approached Hebrew texts for theological rather than mystical reasons, there wasn't any notoriety attached to this study. He was able to advocate for the idea that the texts ought to be read in their original form to be understood. Before Bacon, it seems that few if any gentiles devoted energy to studying Hebrew-- Bacon doesn't convince everyone, but there's a steady trickle of interest over succeeding centuries.

Later, Protestants took a tremendous interest in the original text of the Old Testament. One notable student was Isaac Newton, who applied his massive intellect in equal parts to natural science-- physics and mathematics most famously- and to speculative religious studies. He apparently learned a fair amount of Hebrew, but that wouldn't have been the thing that got him in trouble. Although it wasn't common, people certain understood the idea of learning Hebrew to read the Old Testament.

What could have gotten Newton condemned as a heretic was his Arianism (no connection with "Aryans")-- this is an early Church heresy associated with a priest in Alexandria, Egypt named Arius -- his devotion to a conception of God that the Church had rejected in 4th century.

So knowing Hebrew for scriptural study would have been largely unknown in the early medieval period, becoming more common later and into the Reformation and Renaissance.

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Sources:

Milton, Newton, and the Implications of Arianism

Isaac Newton learns Hebrew: Samuel Johnson's Nova cubi Hebræi tabella

Roger Bacon's Greek and Hebrew Grammars

Early English Hebraists. Roger Bacon and His Predecessors

Magic and Divination at the Courts of Burgundy and France

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