The issue persisted for a long time.

Emojis in kconsole are displayed as blocks(cubes) even though the noto-font-emoji had been installed. I found a solution today

Original Solution

Insert the following lines to /etc/font/fonts.conf inside the <font-config> tag

<match target="font">
		<test name="family" compare="contains">
			<string>Emoji</string>
		</test>
		<edit name="hinting" mode="assign">
			<bool>true</bool>
		</edit>
		<edit name="hintstyle" mode="assign">
			<const>hintslight</const>
		</edit>
		<edit name="embeddedbitmap" mode="assign">
			<bool>true</bool>
		</edit>
	</match>