Note:

None of the Filesystem client layer is official API.

You can use it, but per non-API, it is subject to change at any time.

For example, here is a snippet of code that might help.

    protected boolean hasUncheckedInChangesInWorkspace(IProgressMonitor monitor) {
        boolean uncheckedInChangesExist = false;
        IWorkspace workspace = getWorkspace();
        if (workspace != null) {
            ILocalChangeManager lcm = FileSystemCore.getSharingManager().getLocalChangeManager();
            ISharingManager sm = FileSystemCore.getSharingManager();
            Collection<ISandbox> sandboxes = sm.getRegisteredSandboxes();
            SubMonitor subMonitor = SubMonitor.convert(monitor, sandboxes.size());
            outter: for (ISandbox sandbox : sandboxes) {
                Collection<? extends IConfigurationDescriptor> loadedComponents = null;
                try {
                    loadedComponents = sandbox.allLoadedConfigurations(subMonitor.newChild(1));
                } catch (FileSystemException exception) {
                    // TODO log exception
                }
                for (IConfigurationDescriptor loaded : loadedComponents) {
                    if (loaded.getConnectionHandle() instanceof IWorkspaceHandle) {
                        IComponentHandle component = loaded.getComponentHandle();
                        ILocalChange[] localChanges = lcm.getPendingChanges(workspace, component, sandbox);
                        if (localChanges.length > 0) {
                            uncheckedInChangesExist = true;
                            break outter;
                        }
                    }
                }
            }
        }
        return uncheckedInChangesExist;
    }