I’m counting any title of an independent nation, so some dukes are in the tally.
It’s difficult to say how many monarchies existed on the planet a century ago. In the regions of Asia and Africa colonized by European powers, many indigenous nations had monarchs, but their status is hard to determine. India, for example, consisted of an enormous number of principalities and other political entities with their own local rulers, equipped qith some degree of internal autonomy but united under the British colonial rule. The situation in Arabia was similar; many formally sovereign states came under the protectorate of some European power. It’s largely a matter of definition which entity is counted as a state and which isn’t.
Well, you can put these on the list:
England
Canada
Australia
New Zealand
Jamaica
Barbados
Bahamas
Grenada
Papua New Guinea
Solomon Islands
Tuvalu
San Lucia
Saint Vincent and the Grenadines
Antigua
Barbuda
Belize
Bermuda
Saint Kitts and Nevis
However, these independent nations (commonwealth realms) are all ruled by one monarch: Queen Elizabeth II.
Over the past 54 years, these former subjects of Queen Elizabeth II have since become…well, see the descriptions in parenthesis.
Pakistan (Federal Democratic Republic)
Malta (Republic)
Trinidad and Tobago (Liberal Democracy)
Mauritius (Parliamentary Representative Democratic Republic)
Ghana (Presidential Representative Democratic Republic)
Malawi (Presidential Representative Democratic Republic)
Gambia (Presidential Republic)
Fiji (Parliamentary Representative Democratic Republic)
Sri Lanka (Democratic Socialist Republic)
Guyana (Republic)
India (Sovereign, Socialist, Secular, Democratic Republic)
Ireland (Parliamentary Republic)
Kenya (Presidential Representative democratic Republic)
Nigeria (Federal Republic)
Sierra Leone (Republic)
South Africa (Unified Republic)
Tanzania (Federal Presidential Democratic Republic)
Uganda (Presidential Republic)
This covers a bunch of nations with and no-longer-with royalty, but of course, they all had one monarch either currently or in the past 54 years.
This is all summarized from various sources on the web including Wikipedia.
There are a number of European countries that are now republics, but still have people using noble titles (at least socially) without those titles being recognized by the government. In Germany for example titles have simply become surnames.
The following countries were more or less independent in 1906, and had monarchs, but either no longer exist or don’t have monarchs today: Afghanistan, Austria-Hungary, Bulgaria, China, Ethiopia, Germany, Greece, Iran, Italy, Korea, Portugal, Romania, Russia, Serbia, Montenegro, and the Ottoman Empire.
Beyond that, per Schnitte, there were a slew of monarchs in 1906 who were subservient to some greater colonial or imperial power, from the King of Bavaria to the Prince of Hyderabad. In the century since, a few of these (Swaziland, Tonga) have become full-fledged monarchs when their countries gained independence, but others (Germany, India) have seen their “thrones” abolished.
Nitpick - England is not a sovereign state. Strictly speaking there is no Queen of England, hasn’t been since the union with Scotland in 1707. She’s Queen of the UK, as well as the other places you list.
One person, but different crowns. She is “Queen of Australia”, “Queen of Canada”, etc, and these are quite separate from her role back home.