Whom of the following has not propounded the learning theory?

A learning theory is a systematic explanation of the PROCESS by which learning occurs — it explains HOW behaviour or cognition changes as a result of experience. This is different from a taxonomy, which is a classification scheme for organising objectives or outcomes, not an explanation of the learning process itself.

Checking each name against this criterion:

• Thorndike proposed Connectionism (the Law of Effect), explaining learning as the strengthening of stimulus-response bonds through trial and error.

• Skinner proposed Operant Conditioning, explaining learning as behaviour shaped by reinforcement and punishment.

• Kohler proposed Insight Learning (Gestalt psychology), explaining learning as a sudden reorganisation of perception rather than gradual trial and error.

• B.S. Bloom did not propose a theory of how learning occurs. He led the classification of the cognitive domain of educational objectives, now known as Bloom's Taxonomy; he later co-authored the affective-domain taxonomy with Krathwohl and Masia, while the psychomotor domain was classified separately by other scholars — this is a framework for objectives, not a mechanism of learning.

Cross-checking against the concept: three of the four names explain a mechanism of learning; only Bloom's contribution classifies objectives instead. So Bloom is the one who has not propounded a learning theory.