The standard four elements are the subject compared (mushabbah), comparative model (mushabbah bihi), ground of resemblance (wajh al-shabah) and comparison particle (adat al-tashbih). The first two are called the “two terms” of the simile.
In “knowledge is like light in guidance,” knowledge is the subject, light the model, guidance the shared quality, and kāf the particle. Identifying these elements shows exactly which attribute is being illuminated by the analogy.