$$\sqrt{88+32\sqrt{6}}-2\sqrt{6}$$
$$= \sqrt{88+2\sqrt{16\cdot 32 \cdot 6}} - 2\sqrt{6}$$
$$= \sqrt{88+2\sqrt{3072}} - 2\sqrt{6}$$
$$= \sqrt{(16+12)^2} - 2\sqrt{6} = 28 - 2\sqrt{6}$$