[Grammar] How can you determine that if a person is optimistic or pesemistic ?

[sania-baharat]

Hello,
Are these sentences wrong?

How can you determine that if a person is optimistic or pesemistic ?
How do you know that whether she tells truth or not?

I don't know when we should use "that". Could you please help me? Can we use "that" with "if" and all "wh-words"?

 

[Matthew Wai]

I think we can't use 'that' before those words.

 

[Rover_KE]

[STRIKE]pesemistic[/STRIKE] pessimistic