What is the value of a mandolin used by my grandmother at school in about 1908 inside it says achille lanfranco e figlio fabricanti di mandolini mandole e liuti vico secchia no 41 napoli anni 189?

The value of your grandmother's mandolin would depend on its condition, demand for vintage mandolins, and any unique features it may have. Achille Lanfranco e Figlio was a well-known Italian mandolin maker in the late 19th century, so it could have some value to collectors or musicians interested in historical instruments. A professional appraisal or consultation with a vintage musical instrument expert would provide you with a more accurate estimation of its value.