Filter in Wireshark for TLS's Server Name Indication field
ssl.handshake.extensions_server_name
Shawn E's answer is probably the correct answer but my wireshark version doesnt have that filter. Following filters do exists, however:
To check if the SNI field exists:
ssl.handshake.extension.type == 0
or
ssl.handshake.extension.type == "server_name"
To check if an extension contains certain domain:
ssl.handshake.extension.data contains "twitter.com"
Newer Wireshark has R-Click context menu with filters.
Find Client Hello with SNI for which you'd like to see more of the related packets.
Drill down to handshake / extension : server_name details and from R-click choose Apply as Filter
.
See attached example caught in version 2.4.4