Filter rows based on Where condition AND-OR ?

Why do you want Dynamic sql?

Try the below:

create proc sp_test(@Addnedum int = NULL,@Claimno int = NULL,@Desc int=null)
as
Begin
        Set @Addnedum = (Select Case when LEN(LTRIM(RTRIM(@Addnedum)) = 0 Then NULL Else @Addnedum End)
        Set @Claimno = (Select Case when LEN(LTRIM(RTRIM(@Claimno)) = 0 Then NULL Else @Claimno End)
        Set @Desc = (Select Case when LEN(LTRIM(RTRIM(@Desc)) = 0 Then NULL Else @Desc End)
        
        Select * From Tablename where
        AddendumNo = ISNULL(@A1,AddendumNo) and 
        ClaimNo = ISNULL(@B1,Claimno) and
        Description = ISNULL(@C1,Description)
End

Exec sp_test @Addnedum = 'A1'