What is the name of the guru who teaches Aang about chakras?

The guru who teaches Aang about chakras is Guru Pathik.

Aang meets Pathik at the Eastern Air Temple during Book Two: Earth. Pathik explains that the Avatar State can be controlled by opening seven chakras, each connected to a different emotional or spiritual blockage. His lesson turns the Avatar State from an uncontrolled defense mechanism into a discipline Aang might eventually enter at will.

The final chakra requires Aang to release his earthly attachments. Aang struggles because his feelings for Katara are central to his identity and motivation. When he senses that Katara is in danger, he abandons the lesson before completing the process. This is why he cannot fully control the Avatar State at that point in the story.

Pathik is sometimes confused with other mentors, including Monk Gyatso, who raised Aang, and Avatar Roku, who guides him spiritually. Pathik is specifically the sadhu who teaches the chakra lesson; he also encounters the separated Appa and directs him toward Ba Sing Se.