The Russian attack on Kyiv likely consists of a main effort aimed at enveloping and ultimately encircling the city from the west and a supporting effort along the axes from Chernihiv and Sumy to encircle Kyiv from the east.
I'm not sure if "effort" means "a serious attempt" or "a piece of hard work" and if "along" means "from one end towards the other end of something".
It's "supporting effort" and it means "an effort to support." "Along the axes" means each axis will have this "supporting effort."
"Axes" is just plural for "axis."
"effort" alone means: "a vigorous or determined attempt" according to oxford languages. And, in this case they are talking about a "war effort" since they are at war. A definition from Wikipedia is "In politics and military planning, a war effort is a coordinated mobilization of society's resources—both industrial and human —towards the support of a military force."
The entire sentence could instead be phrased like so:
The Russian attack on Kyiv likely consists of a main effort aimed at enveloping and ultimately encircling the city from the west along with a supporting effort from Chernihiv and Sumy to encircle Kyiv from the east.
"Axes" is not necessary; it just emphasizes the direct path from one city to the next, but that can be inferred.
