NONculstered Index not fire when i use or clause

i have jobs table

jobid primary key

jobcode (nonclustered index)

jobname (nonclustered index)

so

when i run my script as following:-

---case (1)-- in this case query use nonculstered index

declare @x int;

set @x=1;

select * from Jobs
where
 @x=0 and ( jobcode='j' or jobname='j') 

--case (2)-- in this case query not  use nonculstered index and performance be slow

declare @x int;

set @x=1;

select * from Jobs
where
 (@x=0 and ( jobcode='j' or jobname='j') )

or

(@x=0 and  jobcode='j' )

so what can i do to make case (2) use nonclustered index?

case (1)

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case (2)

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