I have a railway reservation in sleeper from Jaipur to Pune and boarding point at Ratlam. Will I be allowed to take my seat at Ratlam OR the TT will cancel it and allocate to others?
You'll be allowed to take the seat at Ratlam.
When the reservation chart will be generated, you will be listed as passenger boarding from a different station than the starting point. Someone else might be at your set from Jaipur to Ratlam.
TTE has the reservation chart which has all the information about passengers boarding from non-starting point stations.