To show sequencing between all tasks (i.e., predecessor/successor relationships and dependency flow), the PM should provide a project network diagram. A summary Gantt chart is great for high-level timelines and major bars, but it can hide the detailed dependency logic that explains why tasks occur in a particular order and how delays propagate. In the CompTIA Project+ objectives, "Project network diagram" is explicitly listed among the key tracking charts/diagrams used to inform project decisions (alongside Gantt and milestone charts).
The other choices don't match the need. A fishbone (Ishikawa) diagram is a root-cause analysis tool for quality issues, not for schedule dependencies. A burndown chart is used mainly in Agile to show remaining work over time, not task-to-task sequencing. A milestone chart highlights key dates, but it doesn't show the detailed dependency chain between tasks.
So, to satisfy the team's request for full sequencing visibility, the PM should share a project network diagram.