they wanted to hear

[Joseph ma]

He told his parents what they wanted to hear that he would help his brother with his school project.

Should there be a comma after "hear" or is there is no punctuation needed for this sentence?

 

[5jj]

Should there be a comma after "hear"

Yes.

 

[jutfrank]

You definitely need some kind of punctuation there, yes. I'm a big fan of the dash:

He told his parents what they wanted to hear—that he would help his brother with his school project.

It works much better than a comma in this sentence.