Learn Turkish: İki öğrenci yorgun. - Two students are tired.

In Turkish, when you use a specific number before a noun (like iki for two), the noun always stays in its singular form. You say iki öğrenci (literally 'two student'), and never iki öğrenciler.

Where is the word for 'are' in this sentence?

Turkish often leaves out the 'to be' verb (am, is, are) in the present tense for the third person (he, she, it, they). The sentence is literally just İki öğrenci yorgun (Two student tired), but it translates to 'Two students are tired'.

Does the adjective yorgun change if there is more than one student?

No. In Turkish, adjectives do not get plural endings to match the noun they describe. The adjective stays as yorgun (tired) no matter how many students there are.