Dual citizenship

Contact the Scottish consulate and ask.

If your parents were British citizens (by birth) at the time of your birth, then you may already be a British citizen by descent. In that case, you would need to fill out an application for a UK passport, supplying documentary proof as required. As Jespah says, you need to approach a British consulate, embassy or high commission.

There is no such thing (yet!), as Scotland is part of the nation called the United Kingdom Of Great Britain and Northern Ireland.

My grandparents were born in Scotland, but my parents were born in 1919.
Sounds a bit like
"Do you walk to school or carry your lunch?"

The "but" is your own invention, as far as I can see.

Another question wpuld be: does the country, where you live now. allow dual citizenship.

Sorry - I rattled that off too fast. Of course you're right.

Most developed countries such as US, UK, Australia, Switzerland have no restrictions on holding dual nationality.

Dual citizenship had previously been banned in the United States, but in 1967 the US Supreme Court struck down most laws forbidding dual citizenship.

However, the US government remained disdainful of dual citizenship for some time. To this day, candidates for US citizenship through naturalization are forced to renounce their previous citizenship at the United States naturalization ceremony. This renunciation may well not be recognized by the candidate's country of origin, resulting in no loss, in that country's eyes, of the first citizenship.

US citizens by birth who become aware of existing citizenship of another country, e.g. by parentage or ancestry, or who live in another country and qualify for naturalization in that other country, face no bar to dual citizenship, and do not need to seek permission from the US Government before ratifying that citizenship e.g. by obtaining a passport or undergoing naturalization.

US citizens who hold dual or multiple nationality are required to use their US passports when entering or leaving the US, and usually when entering or leaving another country where citizenship is held, use of the passport of that country is required.

(I have a cousin who has triple citizenship, Canada, USA, and UK. Many people have more than that.)

Countries that either forbid or restrict dual citizenship:

Andorra, Austria, Azerbaijan ,Burma, Bahrain, Botswana, Japan, China ,Czech Republic, Denmark, Fiji,India,Indonesia, Ecuador, Estonia, Iran, Poland, Papua New Guinea, Brunei, Japan, Peru, Kuwait , Kenya, Kazakhstan, Chile, Kiribati, Poland, Korea, Kuwait, Denmark, Latvia,Singapore, Slovakia, Ecuador, Lithuania, Solomon Islands ,Fiji ,Malaysia, Mauritius, Netherlands, United Arab Emirates (UAE), Romania, Thailand, Mexico, Nepal, Venezuela, Norway, Zimbabwe, Mauritius, Myanmar, Nepal

Pakistan:

Pakistan allows dual citizenship only with the below countries
United Kingdom
Italy
France
Belgium
Iceland
Australia
New Zealand
Sweden
United States
Ireland
Netherlands
Switzerland
Canada
Egypt
Jordan
Syria

Spain

Allows dual citizenship with some Latin-American countries Argentina, Bolivia, Chile, Colombia, Costa Rica, the Dominican Republic, Ecuador, Guatemala, Honduras, Nicaragua, Paraguay, Peru and Uruguay, Andorra, Portugal, the Philippines and Equatorial Guinea.

Totally correct. But since I don't know, where Donnat lives and what nationality he/she has ...
(The former Prime Minister of the [German] state of Lower Saxony, David McAllister [Clan: MacAlister], is of British and German nationality.)