Learn Croatian: Gledaše li grof svijećnjak? - Was the count looking at the candlestick?

Gledaše is the 3rd person singular of the imperfect tense (imperfekt). It is a simple past tense used strictly for continuous or repeated actions. In modern Croatian, the imperfect is highly archaic and mostly encountered in literature, poetry, or historical settings (which fits a sentence about a count). In everyday speech, you would just use the perfect tense: Je li grof gledao svijećnjak?

How is the imperfect form gledaše constructed from the verb gledati?

For imperfective verbs where the infinitive ends in -ati (like gledati), the imperfect endings are -ah, -aše, -aše, -asmo, -aste, -ahu. Since the subject grof is "he" (3rd person singular), we take the infinitive stem gled- and add the 3rd person suffix -aše.

Why do we use just li for the question instead of the usual je li?

You use je li with compound tenses, like the perfect, because je is the auxiliary verb. Because the imperfect is a simple, one-word tense, it doesn't use an auxiliary verb. To form a yes/no question with a simple tense, you place the conjugated main verb first, followed immediately by the question particle li.

Since svijećnjak looks exactly like its dictionary form, is it in the nominative case here?