How to get the year in between two dates

This is not going to be the best looking query but here are some things to get you started.

Before attempting to put it into a query for your table use an IF[^] statement to map out what you want to happen. For example:

declare @LeavStart date = '28-Dec-2015'
declare @LeaveEnd date =  '05-Jan-2016'

if [the years are the same]
	select datediff(dd, @LeavStart, @LeaveEnd)
else
begin
	declare @EndStartYear date -- this will be the last day of the first year
	declare @StartEndYear date -- this will be the first day of the 2nd year

	[Calculate the value of @EndStartYear]
	[Calculate the value of @StartEndYear]

	select datepart(yy, @LeavStart), datediff(dd, @LeavStart, @EndStartYear) + 1
	union
	select datepart(yy, @LeaveEnd), datediff(dd, @StartEndYear, @LeaveEnd) + 1
end

I've left the bits between the square brackets for you to do, but you may find these links useful
DATEPART (Transact-SQL)[^]
Some Common Date Routines - SQLServerCentral[^]

Getting that into a single query against your table is more difficult because of the UNION that is sometimes required. I ended up doing something like this with a Common Table Expression[^]

insert into emp values
('28-Dec-2015','05-Jan-2016'),
('28-Dec-2015','31-Dec-2015'),
('21-Dec-2014','31-Mar-2016')

;with results as -- this is defining my CTE
(
    select empId, LeaveYear = datepart(yy, LeavStart), 
	Y1 = CASE WHEN [the years are the same] THEN
	     [The difference between the dates]
	ELSE
	     [The difference between the start date and the end of that year]
	END
    FROM emp

    UNION

	select empId, datepart(yy, LeaveEnd), 
	     Y1 = CASE WHEN [the years are the same] THEN NULL -- Note!
	ELSE
	     [The difference between the start of the 2nd year and the end date]
	END 
	FROM emp
)
select * from results where Y1 IS NOT NULL
ORDER BY EmpId, LeaveYear

Note the use of the NULL value so that only one row is returned when the dates are in the same year. Watch out for having to add +1 to make the dates inclusive.
And have a look at what happens for my sample data where empId = 3. You may need to sort that out as well.
These are the results I got:

1	2015	4
1	2016	5
2	2015	3
3	2014	11
3	2016	91

If you want them to look like this instead

1	2015	4   2016	5
2	2015	3
3	2014	11  2016	91

Then you will find this link useful - Simple Way To Use Pivot In SQL Query[^]