"Todo el tiempo supiste cómo tocar la guitarra" is correct.

Yo diría "todo este tiempo sabías cómo tocar la guitarra" The differences between "sabías" and "supiste". "sabias" is a form from the "pretérito imperfecto" in Spanish, and the other one "supiste" comes from the "pretérito perfecto simple". Our "preterito perfecto" is your "present perfect" the uses are quite similar. The other one "preterito imperfecto" is used when we are atalking about the past but we don´t know when somenthing happened (if it was yesterday or a week ago). To me both sound the same, but I think is more natural to say "sabías", not many people in Spain would say the other option (but Could be). I wished I helped you¡¡

Gracias a ustedes, esto me ayuda mucho :)

"Todo ESTE tiempo supiste como tocar guitarra?" is also correct Both forms "sabias and supiste" are correct