OK, here are a few of the things you're going to see most often.
US dimes, quarters, half dollars, & dollars dated up to 1964 are 90% silver (except some early dates you're not likely to see ; similarly there are
Half Dimes & two different kinds of silver 3-cent pieces, not to be confused with 3-cent nickels...). US half dollars dated 1965 to 1969 are 40% silver. Panamanian coins are identical to US, as are Cuban in general.
Canadian five-cents (small, not nickel-sized), ten-cents, twenty-five-cents, fifty-cents, & dollars dated up to 1921 are sterling silver (92.5%). After that, until 1967, they are 80%. 1967 can be either 80% or 50%, & there's no easy way to tell them apart ; 1968 are either 50% silver or pure nickel, which is magnetic. After that the circulation coins are not silver. If you see Newfoundland coins, they are pretty much all sterling in the 5-10-25-50 denominations.
Great Britain coins of three pence (small, not the nickel-sized yellow ones), six pence, one shilling, two shillings (floring), two and a half shillings (half crown) & five shillings (crown) dated up to 1921 are sterling ; after that, up to 1945, they are 50% silver. There are other silver denominations, but you're not likely to see them. The same goes for New Zealand & most of the other countries on the pound system, except for the New Zealand crown of 1949 (50%), & the Bermuda crowns of 1959 (sterling) & 1964 (50%). Irish shillings, florins, & half-crowns are 75% silver up to 1943, & the very thick 10-shilling piece of 1966 is 83.3%. Australian coins of the denominations mentioned are sterling up to 1945, then 50% until decimalization. The one-year round 50-cent piece of 1966 is 80% silver. South Africa is 80% silver up until 1950, 50% thereafter until some time after the abandonment of the pound in favour of the rand.
Mexico is all over the map, with peso coins of as little as 10% silver in late dates, & some recent new-peso coins in bimetallic, with a brass ring & a silver center.
Japanese 100-yen pieces are 64% silver from 1957 to 1966.
Larger Dutch coins (1/2, 1, 2 1/2 gulden) are 94.5% silver from 1840 to 1917, 72% thereafter until 1967. The smaller pieces (5, 10, 25 cents) are mostly 64% silver until 1945.
I can't emphasize enough that there are lots more out there.