The SAI of which Pacific Island nation was the Secretary-General of SPASAI until the mid-1990s?

Tonga.

Which is better for retaining knowledge, gradual learning built up over time or intensive learning over a short period?

Gradual learning built up over time.

“When information is accessed gradually over time rather than in a single sitting, it is remembered better. Working professionals often space their training so that they do a section at a time to work around a busy schedule. A likely added benefit of longer exposure to learning materials is enhanced retention. eLearning platforms enable educators to incorporate interactive exercises, quizzes, games, and forum discussions to maintain engagement throughout the training.”

Read more: eLearning: A response to COVID-19 and the future of workplace training