Is Wesen der, die or das?

The correct German article for Wesen is das. The noun Wesen is Neuter. So you always say: das Wesen. Learn the article together with the noun — German nouns don't follow predictable gender rules most of the time.

The plural of Wesen is: die Wesen. In the plural, every German noun takes the article "die". So: die Wesen. Example: ein Wesen → zwei Wesen.

Correct: die Wesen. The form "die Wesens" is wrong. The plural of das Wesen is die Wesen. In the nominative plural, you always use the article "die".

das Wesen follows the four German cases. Nominative: das Wesen, Accusative: das Wesen, Dative: dem Wesen, Genitive: des Wesens. In plural: die Wesen / den Wesen. Learn these forms together with the noun.

The genitive singular of das Wesen is: des Wesens. The genitive plural is der Wesen. German uses the genitive to express possession or belonging. Example: die Farbe des Wesens.

The dative plural of Wesen is: den Wesen. In German, dative plural nouns usually end in "-n". So you say: "mit den Wesen". Use this case after prepositions like mit, von, bei, zu.

Wesen is a noun and must be capitalized in German. You'll find example sentences above for each case. The article das stays the same in nominative singular but changes in other cases. Practice declension in your own sentences.

Yes, Wesen is a noun (also called a substantive). German nouns are always capitalized. The article for Wesen is das. Every German noun has a fixed article you must memorize.