Why didn't Yoda further investigate why Qui Gon Jin's Force Ghost screamed "Anakin, nooo!", and simultaneously felt a disturbance in the Force when Anakin killed the Sand People?
According to the film's official novelisation, Yoda had a whole bunch of stuff going on in that scene. Notably, he was extremely surprised to learn that survival of the spirit after death was possible.
It was Qui-Gon. Yoda knew that it was Qui-Gon. But Qui-Gon was dead, had become one with the Force! One could not retain consciousness and sense of self in that state; one could not speak from beyond the grave.
But Yoda had heard the ghostly call, and in his deep meditative state, his thoughts focused as precisely as they had ever been, the Jedi Master knew that he had not been mistaken.
He wanted to focus on that, then, perhaps to try to follow that call back to the ghostly source, but he could not, overwhelmed again by the surge of rage and pain and… power.
He made a noise and lurched forward, then came out of his trance as his door opened and Mace Windu rushed in. “What is it?” Mace asked. “Pain. Suffering. Death! I fear something terrible has happened. Young Skywalker is in pain. Terrible pain.”
He didn’t tell Mace the rest of it, that somehow Anakin’s rush of agony manifesting in the Force had tapped into the spirit of the dead Jedi Master who had discovered him. Too much was happening here. That disembodied familiar voice hung profoundly in Yoda’s thoughts. For if it was true, if he had heard what he was sure he had heard… - Attack of the Clones - Official Novelisation
Since the next scene takes us straight into the action on Geonosis (followed by a jump straight into Revenge of the Sith, several years later) we're forced to conclude that Yoda did ask Anakin about it, and Anakin just outright lied to him:
Palpatine and Padmé were the only ones who knew about the revenge he had taken. Padmé had been horrified as much by Anakin’s grief as by what he had done; Palpatine called the killings “regrettable.” - Revenge of the Sith - Junior Novelisation