A 30 years old male presented with silvery scales on elbow and knee, that bleed on removal. The probable diagnosis is –
Morphology of papules/plaques in various papulosquamotas disorders

Psoriasis - Erythematous papules and plaques on extensors (elbow & knee
Lichen planus - Violaceous papules with Wickham's striae an flexural surface
Pityriasis rosea - Annular plaques on Trunk
Seborrheic dermatitis - Yellowish, follicular papules on scalp and face 
Pityriasis rubra pilaris - Erythematous follicular papules on Trunk & dorsum of hand
Secondary syphilis - Dusky erythematous papules
Pityriasis lichenoides et varioliformis acuta - Erythematous edematous papules surmounted by vesicles/crust

Coming to question
Clues in this question are :-

Characterstic scales → silver scale
Involvement of elbow & knee
Bleeding on scale removal → Auspitz sign
Pityriasis
Seborrhoeic dermatitis
Psoriasis
Secondary syphilis