You determine the pH range of various indicators from either a table or a chart.
I hope you aren't expected to memorize the pH ranges of the indicators.
In a test situation, your instructor should give you a table or a chart with the values.
For a homework assignment, you might have to look them up in your text or on-line.
Litmus has such a wide pH range that it is useful only for determining if a substance is acidic or basic.
Indicators used in titrations usually change colour over a range of 2 pH units.
Here's a chart that shows the pH ranges of some common indicators.