-- sample TABLE
DECLARE @cell TABLE
(
	ID	int identity(1,1),
	cell	varchar(10)
)

-- Generate some sample data
INSERT INTO @cell (cell)
SELECT	cell = CHAR(ASCII('A') + c.NUMBER) + CONVERT(varchar(10), n.NUMBER)
FROM	F_TABLE_NUMBER_RANGE(0, 6) c
	CROSS JOIN F_TABLE_NUMBER_RANGE(1, 6) n
ORDER BY c.NUMBER, n.NUMBER

DECLARE	@ref_cell varchar(10)

SELECT	@ref_cell	= 'D4'

-- Query
;WITH cell (cell, row, col)
AS
(
	SELECT	cell,
		row	= row_number() OVER (PARTITION BY dbo.fnFilterString(cell, '[A-Z]') ORDER BY cell),
		col	= row_number() OVER (PARTITION BY dbo.fnFilterString(cell, '[0-9]') ORDER BY cell)
	FROM	@cell c
)
SELECT	c.cell
FROM	cell c
	INNER JOIN cell r	ON	c.row	>= r.row - 1
				AND	c.row	<= r.row + 1
				AND	c.col	>= r.col - 1
				AND	c.col	<= r.col + 1
WHERE	r.cell	= @ref_cell
ORDER BY c.cell