Point it to the Table

DLookup("FieldName", "TableName","WHERECLAUSE")

If this doesn't help, you're going to have to provide more information on what you are trying to achieve:

Read Only Text Box Name
Table Name
Combo Box Name

Maybe some screenshots?

DLookup

So I have tables t_student, t_joint_student_exam, t_exam, t_level_exam.
the tables are like that
t_student : id_student, first_name_student, last_name_student
t_joint_student_exam : id_joint, fk_student, fk_exam
t_exam : id_exam, name_exam, fk_level_exam
t_level_exam : id_level_exam, name_level_exam


when I open the form f_student (t_student) I have a button that opens f_list_exam (t_joint_student) that lists every exam (continuous form) for current student.

In that form I want to have a combo box with every exams in a query (I could need it again with an another table where there would be a first name last name joint together)  that has id_exam, name_exam.

there are also a number of text box that aren't modifiable to the user and are automatically updated when a exam is selected.

One of them should show name_level_exam related to that exam

Ok so I found a way to do it using dlookup in the query which wasn't working because it wasn't the correct regional separator.
and then using =[CMBBox_name].[Column](x) in the textbox