You can use it after winning the Glacier badge at Snowpoint city.
As far as I'm aware, you need the badge from Canalave City (the sixth) which can be reached after obtaining the Surf HM from Cynthia's grandmother. Hope that helps! - BanetteBrain
The mine badge.
I think it's the 7th badge, i just tried it and i have 6 badges and it failed :/
You have to beat the elite four then go to Kanto and beat all of their gyms to use rock climb.
To find HM 05 Defog, go to the Great Marsh and pick up the pokeballs on the floor until you get it. You'll need the Relic Badge and the Fen Badge to use it. (AKA, Gym badge 4 and 5)
As far as I'm aware, you need the badge from Canalave City (the sixth) which can be reached after obtaining the Surf HM from Cynthia's grandmother. Hope that helps! - BanetteBrain
The mine badge.
One I know is on rout 217 near to where you find rock climb. There are a few items there as well. Warning, you need the canalave gym badge though!
you need to get the 7th gym badge. :)
In Diamond, Pearl, and Platinum, you will find HM08, the device needed to teach Rock Climb, on Route 217, near Snowpoint City. In order to be able to use the move outside of battle, you will need the Icicle Badge from the Snowpoint Gym. In Heart Gold and Soul Silver, you will need to defeat all 16 Gyms before you can use Rock Climb at all. When you conquer the Viridian Gym, Blue will hand you the Earth Badge, which enables you to use Rock Climb outside of battle. Immediately afterwards, Professor Oak will call you, and summon you to his lab. Speak to him there, and he will give you HM08.
You will need the 7th and 8th Gym Badge, which belonged to Candice of Snowpoint City and Volkner of Sunyshore City.
I think it's the 7th badge, i just tried it and i have 6 badges and it failed :/
U need 7 badges to get it
you cant get it.there's another HM called rock climb near snowpoint city but you need the sunnyshore city gym badge to use it outside of battle to get in sunnyshore city but to get in sunnyshore city you need to get palkia at the top of mt.coronet
You have to beat the elite four then go to Kanto and beat all of their gyms to use rock climb.
You need to use rock climb to get to his house.
you need to be able to climb trees