People already knew where Wakanda was. Just not that it was super advanced.

I honestly have no clue. Asgard probably knew about how advanced Wakanda was but there is no explanation to how to Thor knew that there was the battle for the Mind Stone going on there specifically. My best answer is because plot.

groot told him

@Bund and how did Groot know?

That is one mystery that has left me confused. Like also how come he is super powerful in Ragnarok, but we don't see any of that in Infinity War? I know that it opened with the battle over and Thor defeated, but we can tell that he didn't do too much to try and stop it.

the secret is in groot's gameboy. everyone assumed he was playing game.

Thor went to his 'magic jacuzzi' again, which he previously used in Avengers: Age of Ultron, to find out where is the attack happening. Lol.

@Bennyhef234: The problem when you are extremely powerful is the collateral damage that you can cause. It's possible that Thor could not unleash his full power because it would have hurt other Asgardians or damaged, and even destroyed, the Statesman.

And even when releasing his power, Thanos and the Black Order are formidable fighters, who had little regard for the damage they could cause... The only one they needed alive was Loki to take the Tesseract from him.

I think that whenever Thor told Heimdall to open the Bifrost, it opened at the exact spot that Thor or the caller was standing. So it can be locked onto a person. Since Stormbreaker can summon the Bifrost Thor only had to tell it which person to lock onto and there he was, fighting in Wakanda.