I need help with a SQL Query

You can do that by giving us table names, field names to be updated, etc. Any relevant information we need to built a workable example.

Also see: https://www.experts-exchange.com/articles/18499/Top-10-Ways-to-Ask-Better-Questions.html

Here is one example

UPDATE Test1.dbo.Employee
SET DeptID = emp2.DeptID
FROM Test2.dbo.Employee as 'emp2'
WHERE
   Test1.dbo.Employee.EmployeeID = emp2.EmployeeID

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If two tables are involved, you cannot go without a FROM clause. Anything using a different source than the  table to update requires it. With one exception: You can build an updatable view, which obfuscates the table the column is located in - but that has a lot of constraints, and I won't go into the details for that reason.

If you are trying to head towards something e.g. Oracle allows, which is

update (select ta.ca1, tb.cb2 from table1 ta join table2 tb on ta.id = tb.id /* ... */)
set ca1 = cb2

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this cannot be used in MSSQL that way, and anyway it contains a FROM too :D