How did medievals read the Book of Job? Through authoritative commentaries. In the 12th century this was made visible in the "Glossa Ordinaria." You can't read even a sentence without help. Below Job 3 from a late edition, explaining why Job's cursing the day of his birth can not be read literally.
Oxford Bodleian Library MS Laud Lat. 9, fols. 14v-15r (Proverbs); in Lesley Smith, The "Glossa Ordinaria": The Making of a Medieval Bible Commentary (Leiden & Boston, Brill, 2009). Job 1 and 3 from a Biblia Latina cum Glossa Ordinaria (1480/1481 Editio Princeps of Adolph Rusch of Strassburg; facsimile Brepols: Turnhout, 1992)