Acidity of naphthol vs hydroxynaphthoquinone
For naphtol both the acidic and the basic forms have many resonance structures along the two fused benzene cycles. However, in the case of 2-hydroxy-1,4-naphthoquinone, the basic conjugated form creates novel resonance structures that engage the double bond of the quinone cycle as seen in the written resonance structure in the question. The novel resonance structures of the basic forms will stabilize the basic form. 
Therefore, the hydroxyl group in 2-hydroxy-1,4-naphthoquinone has higher tendency to lose the hydrogen ion than the hydroxyl group in naphtol. This explains the higher acidity of 2-hydroxy-1,4-naphthoquinone in comparison with naphtol.