You have to know what your policy is, and its additional cost for jewerly coverage, and its own specific requirements for documentation.
For a separate jewelry rider, it can be about $10 per $1k insured, and it does add up: so, if you insure $10k worth of jewelry you can expect to pay about $100/year. Maybe a little less. This is for no deductible, full replacement value
To me it makes no sense to insure below a certain value point, so figure that out. Example: it may not be a great idea to spend $$ to insure an item with a $100-$500 replacement value; over a few years you wind up essentially rebuying it.
Your insurer can tell you the cost and also what's needed for insuring (i.e., appraisals, which cost to get, or is a website link to its retail figure enough?).