Final answer:
The grammatically correct sentence is 'Vosotros sabéis tocar la guitarra.'
Step-by-step explanation:
The grammatically correct sentence is 'Vosotros sabéis tocar la guitarra.' This sentence is in the second person plural form and uses the correct verb form for 'you all' in Spanish. The verb 'sabéis' agrees with the subject 'Vosotros'.
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