I use sql server 2014.
I have a table in my ManuDB database called (waqf).
I am trying to update the table but not allowed and a message (invalid object name waqf) appears.
I don't know what is the reason although I have a table called waqf.

Because you are executing the statement in Master Database as shown in the snip shot.

select the correct database from drop down list shown in picture or execute the following statement.
USE ManuDB
GO
UPDATE ......
masterdatabase (see the dropdown just above theObject Explorer) - and there's no table of that name in themasterdatabase!