if a student study in aims is eligible for practice with out pg
Not exactly. AIIMS is India's best medical College and someone who has finished mbbs from there is highly knowledgeable, no doubt. But, even with that consideration, hospitals or clinics will prefer someone with a specialisation. MBBS is not enough to make you a trusted doctor nowadays.
You may open your own clinic but people will prefer to go to someone with a specialisation.
You can do academic medicine and clinical research after mbbs. But it's highly advisable to go for a pg. You've come so far, better to go 2 more years to make it all worth it.
Best of luck!