Once you clear Team Rocket out of the Celdon City game room, you get the Silph Scope from Giovanni, (which enables you to see the ghost at the top of Lavender tower). After you battle your way to the top of the tower, you will find more Team Rocket grunts, after defeating them you rescue Mr. Fuji, he then takes you down to his house and he will grant you the Poke-Flute.
(In order to get in to Saffron City you need to have taken the underground tunnel into Celdon City, gotten the tea from the elderly lady on the first floor of the apartments, and given it to the guard blocking the road into Saffron.)
You need to get the Pokeflute.
Use the pokeflute.
If there in the way of your path then use the pokeflute.
Mr fuji has the pokeflute he is at the top of Pokemon tower in Lavender Town.
You need to use a pokeflute.
play the pokeflute to the snorlax in front of it
You have to get a Pokeflute from Mr. Fuji after you rescue him from the Pokemon Tower at Lavender Town.
Use the pokeflute to wake it up then capture it or make it faint.
play pokeflute
In Pokémon Pokémon FireRed and LeafGreen you will encounter a sleeping Snorlax blocking the way. To wake him up you need to get the Pokeflute.
there isn't pokeflute in Pokemon pearl or diamond
Pokeflute is on the Pokemon radio when you are in Johto or Kanto.