Since Juniper deleted the jnxExVlan mib from Junos on the newer EX platforms, you have to use only standard Q-BRIDGE-MIB OIDs:
.iso.org.dod.internet.mgmt.mib-2.dot1dBridge.qBridgeMIB
To get the list of untagged ports on each vlan:
.iso.org.dod.internet.mgmt.mib-2.dot1dBridge.qBridgeMIB.qBridgeMIBObjects.dot1qVlan.dot1qVlanStaticTable.dot1qVlanStaticEntry.dot1qVlanStaticUntaggedPorts
Defined as:
dot1qVlanCurrentUntaggedPorts OBJECT-TYPE
SYNTAX PortList
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The set of ports that are transmitting traffic for
this VLAN as untagged frames."
REFERENCE
"IEEE 802.1Q/D11 Section 12.10.2.1"
::= { dot1qVlanCurrentEntry 5 }
Additiionally, if you want the Q-BRIDGE-MIB to follow the standard syntax (bitmap) for PortList, set this (recommended):
set switch-options mib dot1q-mib port-list bit-map
If you want the Q-BRIDGE-MIB to use the non-standard, Juniper-specific "ASCII comma-separated" port list format, don't set that.