Populate Textbox values to Textbox from unrelated table

Not enough info. How are you getting the data from the database?
What does this mean, "Populate Textbox value to Textbox from unrelated table?"
What type of application are you developing?
Can you please post the code you are using.

Developing a Windows form application using a dataset to access the database.

tblWorkorder has TextboxA to be filled with tblChecklists TextboxB value using buttonclick event.

So you are using a DataSet and a DataTable object to organize your data from the database. So your DataTable may have many rows that were returned by the SQL query.

I am assuming that TextboxA and TextboxB are Windows Form TextBox objects placed on the form. I am also assuming that tblWorkorder and tblChecklists are each a DataTable object that are assigned to the DataSet that hold the data from the database. I can not understand what this means, "tblWorkorder has TextboxA to be filled with tblChecklists TextboxB value using buttonclick event.", can you explain this in a bit more detail?

You are correct on your assumptions...

I need to copy a value from TextboxA on frmExample1 to TextboxB on frmExample2 with an event.

TextboxB.text = TextboxA.text  doesn't work for you?

Thanks for your help!

Not a problem, glad to help.