As of 2004, which of the following cricketers holds the world record of maximum number of sixes in Tests?

The correct choice is: Chris Cairns (New Zealand)

Chris Cairns of New Zealand retired in 2004 with 87 Test sixes, which was then the world record. He had passed Viv Richards (84). Sachin Tendulkar and Wasim Akram had fewer sixes.

Among the given names, the record belongs to Chris Cairns. (Australia's Adam Gilchrist passed him soon afterwards, and in November 2007 he became the first batsman to hit 100 Test sixes.)

Hence the answer is ‘Chris Cairns (New Zealand)’.

Today the record for most Test sixes belongs to England's Ben Stokes.