To find topics or angles for investigative stories try this:

What are your interests?

What are you interested in? For example: culture, technology, health, environment, nature (biodiversity), food, housing, care, development aid, transport/infrastructure, education, sports, work, law, privacy, equal treatment, gender equality, freedom of expression, politics and governance, extremism, defense, worldview or religion.
Where (which place) would you like to go and take a look?
Who would you like to talk to?
Which sources (contacts, documents, data) do you already have?
Did someone give you a tip?

What is in the news?

What is currently in the news in your area of interest?
Who is making noise, and about what? (Pay attention to advice, proposals, warnings, complaints, and protests.)
Who is under scrutiny, and why? (Pay attention to allegations and lawsuits.)
What is being debated in professional circles (professional literature, associations, conferences)?
What questions do current events raise for you?

What changes do you see in your neighborhood, at your school, or at your workplace?
What consequences do global agreements or national policy have for your neighborhood, your city, your university, your company, your association?

What have you experienced yourself recently? (When were you surprised, angry, or afraid?)