Star of David vs emblem

Star of David and emblem both are nouns.

Word	Noun	Adjective	Verb	Adverb
Star of David	Yes	No	No	No
emblem	Yes	No	No	No

As nouns, emblem is a hypernym of Star of David; that is, emblem is a word with a broader meaning than Star of David:

Star of David: a six-pointed star formed from two equilateral triangles; an emblem symbolizing Judaism
emblem: a visible symbol representing an abstract idea

Other hypernyms of Star of David include allegory, hexagram.

Star of David (noun)	emblem (noun)
a six-pointed star formed from two equilateral triangles; an emblem symbolizing Judaism	special design or visual object representing a quality, type, group, etc.
	a visible symbol representing an abstract idea