What is meant by "knowledge" as it appears in the hadiths that mention the virtue of knowledge and the great reward of scholars? Does it refer only to religious knowledge, or does it include other types of knowledge such as biology, physics, electronics, and so on?

The knowledge intended in the texts of praise is the knowledge of the Sharia, derived from the Qur'an and Sunnah. This includes the sciences of the Arabic language, inheritance laws, acts of worship, transactions, legal punishments, and Islamic and linguistic etiquette. It also encompasses the tools for these sciences, such as the principles of Islamic jurisprudence (Usul al-Fiqh) and Tawhid (monotheism). As for other worldly sciences like biology, chemistry, and industrial sciences, they are considered communal obligations (fard kifaya) as long as they do not distract from the obligatory sciences. Military sciences are considered among the foremost and most essential of these sciences.