Unlike in North Korea the JW men in the Ukraine can get a religious exemption (perhaps being required to do medical work during wartime or some other noncombat community service). Note that https://www.refworld.org/docid/57a188544.html (a website of the UN) says the following (the bold face emphasis is mine).
'2. Conscientious Objectors
Sources state that the Ukrainian military allows for alternative
service for conscientious objectors (US 14 Oct. 2015, 5; UN Sept. 2015,
para. 36; Equal Rights Trust Aug. 2015, 192) based on religious grounds
(ibid.; UN Sept. 2015, para. 36). According to information posted on the
website of the Ukrainian Ministry of Foreign Affairs, Article 35 of The
Constitution of Ukraine states that
[n]o one shall be relieved of his or her duties before the State or
refuse to perform the laws for reasons of religious beliefs. In the case
that the performance of military duty is contrary to the religious
beliefs of a citizen, the performance of this duty shall be replaced by
alternative (non-military) service. (Ukraine [2015])
The 2004 summary version of the 1992 Law of Ukraine "'On Alternative
(Non-Military) Service'," as found on the website of the Institute for
Religious Freedom (IRF), a Kyiv-based human rights NGO that assists "in
the realization of freedom of conscience, religion, beliefs and other
related human rights…and dissemination of information on the status of
the law and religious life" in Ukraine (IRF n.d.), states that
[c]itizens shall do alternative service on the enterprises which are
in state or communal ownership or dominant part in the state fund of
which is in the state or communal ownership. Activity of such
enterprises shall be related to social protection of population, health
protection, environmental protection, building, housing and communal
services, and agriculture. Besides, alternative service may be conducted
in medical attendance service in Red Cross organizations of Ukraine.
Labour relations between the citizen who does military service and
enterprise shall be maintained on the basis of written fixed-date labour
agreement. (Ukraine 2004)
Further information on the details of alternative non-military
service could not be found among the sources consulted by the Research
Directorate within the time constraints of this Response.
According to a report by Equal Rights Trust[1], which was written in
partnership with the LGBT Human Right Centre Nash Mir, the religious
groups that are able to claim conscientious objector status, on the
basis that their religious organisations do not allow their members to
bear arms, are: Adventist Reform Church, Seventh Day Adventists,
Evangelical Christians, Evangelical Christian-Baptists, the Slavic
Church of the Holy Spirit (Pokutnyky), Jehovah's Witnesses, the
Charismatic Christian Churches and the International Society for Krishna
Consciousness (Equal Rights Trust Aug. 2015, 192). An excerpt from the
forthcoming (2016) book Free Radicals: War Resisters in Prison, by CJ
Hinke, as found on the website of World Beyond War, a "global nonviolent
movement to end war and establish a just and sustainable peace" (World
Beyond War n.d.b), similarly indicates that in Ukraine, those who are
able to claim religious conscientious objector status are: Seventh Day
Adventists, Baptists, Adventists-Reformists, Jehovah's Witnesses and
Charismatic Christians (ibid. n.d.a).'
https://www.state.gov/reports/2020-report-on-international-religious-freedom/ukraine/ ("An official website of the United States Government") mentions legal cases involving JWs in Ukraine.
https://www.jw.org/en/news/legal/by-region/ukraine/human-rights-conscientious-objectors/ has a news article which says the following (the bold face emphasis is mine). "Ukraine’s high court has affirmed that conscientious objectors have the
right to alternative service even in times of civil unrest and war. This
decision has broad implications for human rights, both in Ukraine and
abroad.
... The courts of Ukraine have recognized that conscientious objection to
military service is a fundamental human right that merits protection
even during military mobilization. It is neither a selfish evasion of
duty nor a threat to national interests and security. In affirming the
rulings of the lower courts, the high court has upheld human rights for
all Ukrainians. Ukraine has set an example for countries that punish
conscientious objectors who refuse military service for reasons of
conscience."