Learn Croatian: Ne mogu vidjeti je li frizura lijepa. - I cannot see if the hairstyle is nice.

In English, we use "if" for both conditions (like "if it rains") and reported questions (like "I wonder if it is raining"). In Croatian, conditional "if" is ako, but for reported yes/no questions where "if" means "whether", you use je li.

Where is the verb in the second part of the sentence (je li frizura lijepa)?

The verb is actually the je in je li! It is the 3rd person singular of biti (to be). The literal translation of the second half is "is [question particle] hairstyle nice".

In everyday speech, could I use da li instead of je li here?

Yes, colloquially you will often hear Ne mogu vidjeti da li je frizura lijepa. However, standard Croatian grammar prefers using je li for these indirect questions, which is exactly what this lesson focuses on.

Just to review, why do we use the infinitive vidjeti here?

Because it follows the modal verb mogu (I can). When you have a modal verb followed by another action, the second verb must be in its infinitive form.