Literally it's "the title of that topic", so "that" here refers to "topic" and should agree with it's case and gender.Originally Posted by tohca
"Темы" is feminine and genitive. So you take "эта" (fem.) (not "это" or "этот"!) and put it into genetive: "этой".
If you want use any masculine noun (for example "раздел") it would be "этого" (masc. gen.), i.e. "название этого раздела".