I got a tattoo. On 32nd day I went for HIV 1/2 & p24 Combo test (CMIA) and its came negative. Is this conclusively? How much I can trust this result.

Trust it. Proper sterilization of tattoo equipment is near-universal today. There is an HIV risk if the needle was recently used by another person. Just how much of a risk getting inked ever was for hepatitis C is unknown; other risky practices run with tattoo culture. Whatever exposure you may have had, the test is reliable at 32 days; human reporting error makes the false-negative rate unknowable.