Unless you have any logic which empties the field when it is reopened, the information should still be shown.
You also may have a UI Policy which hides the field.
You could either change that UI Policy, so that it shows the field when it is not empty, or you could simply change the state to resolved (without saving) to see what is in the field and change the state back.
You could add resolution notes to the activity as well, so you can see it there.
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