Both Questions are Off-Topic
Both questions seem off-topic in various ways. In particular, both questions can be interpreted as career advice in the vein of how to qualify for a given exam---or worse yet, which certification to pursue.
Perhaps more egregiously, https://pm.stackexchange.com/questions/8408/prerequisites-for-pmp-exam is really a "LMGTFY" question. It is a question that could be answered best by reading the PMI requirements for the certification, or asking clarifying questions of the certifying body rather than polling for opinions on the Internet.
Raise the Issue When Needed
Not everyone who visits the site reads every question, especially on topics that don't intrinsically interest them. If you want more participation from the community on questionable questions, downvote or vote-to-close so that it shows up in the review queue as something worth looking into more closely.
I'm not sure if diamond moderators can vote-to-close without unilaterally closing a question. If you can, that might garner more community involvement because it shows that someone is calling for a vote. If you can't vote-to-close as a diamond moderator, downvoting at least pushes it to the top of the "activity" tab of the questions page in a way that people with close-vote privileges are more likely to notice.
Push to the Review Moderator-Tools Queues
Again, I'm thoroughly ignorant of the magical powers granted to diamond moderators. However, taking some action that pushes questionable questions to the Close Votes or Low Quality Posts review queues will certainly draw attention from people with the correct privileges. In addition, users with access to Moderator Tools will have vote privileges on certain types of flagged questions, so that may be an option, too.
I applaud your desire to see more community involvement in closing duplicate and off-topic questions. In my opinion, we just need to leverage the existing Stack Exchange mechanics to make that happen.
Updated Information Extracted from Comments and Discussions
@jmort253 correctly points out some additional information, which I'm pulling up into the answer for posterity.
- Diamond moderators cannot vote-to-close or flag questions without taking direct, unilateral action on a question. However, others with elevated privileges can do so, and are encouraged to use those mechanics when appropriate.
- Diamond moderators can use upvotes and downvotes just like everyone else, which is a great way for them to communicate to non-moderators with voting privileges.
- Editing and answering questions (including retagging) pushes them to the top of the "activity" tab of the questions page, but doesn't seem to impact the position on the "newest" tab.
- Voting doesn't seem to directly correlate to ordinal position on the question tabs, but sufficient downvotes may push questionable questions into the review queues. (NB: This might be a worthy topic to research or ask about on Meta Stack Overflow).
Thanks to @jmort23 for the clarifications.