Следующий код должен отображать ваши документы:
var sql = @"SELECT c.Indice
, c.Name
, ....
, cc.Indice
, cc.CallDateTime
, ....
, rpc.Indice
, rpc.Question1
, ....
FROM Client c
INNER JOIN CallClient cc on c.Indice = cc.Indice
INNER JOIN PollClient pc on c.Indice = pc.Indice";
using (var conn = new SqlConnection())
{
var res = conn.Query<Client, CallClient, ResponsePollClient, DataClient>(sql, (c, cc, pc) =>
{
var d = new DataClient()
{
client = c,
callClient = cc,
pollClient = pc
};
return dc;
}, splitOn: "Indice");
}